diff --git a/app/src/main/AndroidManifest.xml b/app/src/main/AndroidManifest.xml
index 9f9a414930..1383e63659 100644
--- a/app/src/main/AndroidManifest.xml
+++ b/app/src/main/AndroidManifest.xml
@@ -391,6 +391,10 @@
         </intent-filter>
     </activity>
 
+        <activity android:name=".components.settings.app.changenumber.ChangeNumberLockActivity"
+            android:theme="@style/Signal.DayNight.NoActionBar"
+            android:configChanges="touchscreen|keyboard|keyboardHidden|orientation|screenLayout|screenSize"/>
+
         <activity android:name=".components.settings.conversation.ConversationSettingsActivity"
             android:configChanges="touchscreen|keyboard|keyboardHidden|orientation|screenLayout|screenSize"
             android:theme="@style/Signal.DayNight.ConversationSettings"
diff --git a/app/src/main/java/org/thoughtcrime/securesms/PassphraseRequiredActivity.java b/app/src/main/java/org/thoughtcrime/securesms/PassphraseRequiredActivity.java
index eaa3f8109a..63bfe6c738 100644
--- a/app/src/main/java/org/thoughtcrime/securesms/PassphraseRequiredActivity.java
+++ b/app/src/main/java/org/thoughtcrime/securesms/PassphraseRequiredActivity.java
@@ -15,6 +15,7 @@ import org.greenrobot.eventbus.EventBus;
 import org.signal.core.util.logging.Log;
 import org.signal.core.util.tracing.Tracer;
 import org.signal.devicetransfer.TransferStatus;
+import org.thoughtcrime.securesms.components.settings.app.changenumber.ChangeNumberLockActivity;
 import org.thoughtcrime.securesms.crypto.MasterSecretUtil;
 import org.thoughtcrime.securesms.dependencies.ApplicationDependencies;
 import org.thoughtcrime.securesms.devicetransfer.olddevice.OldDeviceTransferActivity;
@@ -50,6 +51,7 @@ public abstract class PassphraseRequiredActivity extends BaseActivity implements
   private static final int STATE_CREATE_SIGNAL_PIN   = 7;
   private static final int STATE_TRANSFER_ONGOING    = 8;
   private static final int STATE_TRANSFER_LOCKED     = 9;
+  private static final int STATE_CHANGE_NUMBER_LOCK  = 10;
 
   private SignalServiceNetworkAccess networkAccess;
   private BroadcastReceiver          clearKeyReceiver;
@@ -153,6 +155,7 @@ public abstract class PassphraseRequiredActivity extends BaseActivity implements
       case STATE_CREATE_PROFILE_NAME: return getCreateProfileNameIntent();
       case STATE_TRANSFER_ONGOING:    return getOldDeviceTransferIntent();
       case STATE_TRANSFER_LOCKED:     return getOldDeviceTransferLockedIntent();
+      case STATE_CHANGE_NUMBER_LOCK:  return getChangeNumberLockIntent();
       default:                        return null;
     }
   }
@@ -176,6 +179,8 @@ public abstract class PassphraseRequiredActivity extends BaseActivity implements
       return STATE_TRANSFER_ONGOING;
     } else if (SignalStore.misc().isOldDeviceTransferLocked()) {
       return STATE_TRANSFER_LOCKED;
+    } else if (SignalStore.misc().isChangeNumberLocked() && getClass() != ChangeNumberLockActivity.class) {
+      return STATE_CHANGE_NUMBER_LOCK;
     } else {
       return STATE_NORMAL;
     }
@@ -243,6 +248,10 @@ public abstract class PassphraseRequiredActivity extends BaseActivity implements
     return MainActivity.clearTop(this);
   }
 
+  private Intent getChangeNumberLockIntent() {
+    return ChangeNumberLockActivity.createIntent(this);
+  }
+
   private Intent getRoutedIntent(Class<?> destination, @Nullable Intent nextIntent) {
     final Intent intent = new Intent(this, destination);
     if (nextIntent != null)   intent.putExtra("next_intent", nextIntent);
diff --git a/app/src/main/java/org/thoughtcrime/securesms/components/settings/app/changenumber/ChangeNumberEnterCodeFragment.kt b/app/src/main/java/org/thoughtcrime/securesms/components/settings/app/changenumber/ChangeNumberEnterCodeFragment.kt
index 713f648366..c34b2ffe18 100644
--- a/app/src/main/java/org/thoughtcrime/securesms/components/settings/app/changenumber/ChangeNumberEnterCodeFragment.kt
+++ b/app/src/main/java/org/thoughtcrime/securesms/components/settings/app/changenumber/ChangeNumberEnterCodeFragment.kt
@@ -2,12 +2,14 @@ package org.thoughtcrime.securesms.components.settings.app.changenumber
 
 import android.os.Bundle
 import android.view.View
+import androidx.activity.OnBackPressedCallback
 import androidx.appcompat.widget.Toolbar
 import androidx.navigation.fragment.findNavController
 import org.thoughtcrime.securesms.R
 import org.thoughtcrime.securesms.components.settings.app.changenumber.ChangeNumberUtil.changeNumberSuccess
 import org.thoughtcrime.securesms.components.settings.app.changenumber.ChangeNumberUtil.getCaptchaArguments
 import org.thoughtcrime.securesms.components.settings.app.changenumber.ChangeNumberUtil.getViewModel
+import org.thoughtcrime.securesms.keyvalue.SignalStore
 import org.thoughtcrime.securesms.registration.fragments.BaseEnterCodeFragment
 
 class ChangeNumberEnterCodeFragment : BaseEnterCodeFragment<ChangeNumberViewModel>(R.layout.fragment_change_number_enter_code) {
@@ -17,9 +19,26 @@ class ChangeNumberEnterCodeFragment : BaseEnterCodeFragment<ChangeNumberViewMode
 
     val toolbar: Toolbar = view.findViewById(R.id.toolbar)
     toolbar.title = viewModel.number.fullFormattedNumber
-    toolbar.setNavigationOnClickListener { findNavController().navigateUp() }
+    toolbar.setNavigationOnClickListener { navigateUp() }
 
     view.findViewById<View>(R.id.verify_header).setOnClickListener(null)
+
+    requireActivity().onBackPressedDispatcher.addCallback(
+      viewLifecycleOwner,
+      object : OnBackPressedCallback(true) {
+        override fun handleOnBackPressed() {
+          navigateUp()
+        }
+      }
+    )
+  }
+
+  private fun navigateUp() {
+    if (SignalStore.misc().isChangeNumberLocked) {
+      startActivity(ChangeNumberLockActivity.createIntent(requireContext()))
+    } else {
+      findNavController().navigateUp()
+    }
   }
 
   override fun getViewModel(): ChangeNumberViewModel {
diff --git a/app/src/main/java/org/thoughtcrime/securesms/components/settings/app/changenumber/ChangeNumberLockActivity.kt b/app/src/main/java/org/thoughtcrime/securesms/components/settings/app/changenumber/ChangeNumberLockActivity.kt
new file mode 100644
index 0000000000..ecc17d0dd4
--- /dev/null
+++ b/app/src/main/java/org/thoughtcrime/securesms/components/settings/app/changenumber/ChangeNumberLockActivity.kt
@@ -0,0 +1,108 @@
+package org.thoughtcrime.securesms.components.settings.app.changenumber
+
+import android.content.Context
+import android.content.Intent
+import android.os.Bundle
+import com.google.android.material.dialog.MaterialAlertDialogBuilder
+import io.reactivex.rxjava3.android.schedulers.AndroidSchedulers
+import io.reactivex.rxjava3.core.Single
+import io.reactivex.rxjava3.kotlin.subscribeBy
+import org.signal.core.util.logging.Log
+import org.thoughtcrime.securesms.MainActivity
+import org.thoughtcrime.securesms.PassphraseRequiredActivity
+import org.thoughtcrime.securesms.R
+import org.thoughtcrime.securesms.keyvalue.SignalStore
+import org.thoughtcrime.securesms.logsubmit.SubmitDebugLogActivity
+import org.thoughtcrime.securesms.phonenumbers.PhoneNumberFormatter
+import org.thoughtcrime.securesms.util.DynamicNoActionBarTheme
+import org.thoughtcrime.securesms.util.DynamicTheme
+import org.thoughtcrime.securesms.util.LifecycleDisposable
+import org.thoughtcrime.securesms.util.TextSecurePreferences
+import java.util.Objects
+
+private val TAG: String = Log.tag(ChangeNumberLockActivity::class.java)
+
+/**
+ * A captive activity that can determine if an interrupted/erred change number request
+ * caused a disparity between the server and our locally stored number.
+ */
+class ChangeNumberLockActivity : PassphraseRequiredActivity() {
+
+  private val dynamicTheme: DynamicTheme = DynamicNoActionBarTheme()
+  private val disposables: LifecycleDisposable = LifecycleDisposable()
+  private lateinit var changeNumberRepository: ChangeNumberRepository
+
+  override fun onCreate(savedInstanceState: Bundle?, ready: Boolean) {
+    dynamicTheme.onCreate(this)
+    disposables.bindTo(lifecycle)
+
+    setContentView(R.layout.activity_change_number_lock)
+
+    changeNumberRepository = ChangeNumberRepository(applicationContext)
+    checkWhoAmI()
+  }
+
+  override fun onResume() {
+    super.onResume()
+    dynamicTheme.onResume(this)
+  }
+
+  override fun onBackPressed() = Unit
+
+  private fun checkWhoAmI() {
+    disposables.add(
+      changeNumberRepository.whoAmI()
+        .flatMap { whoAmI ->
+          if (Objects.equals(whoAmI.number, TextSecurePreferences.getLocalNumber(this))) {
+            Log.i(TAG, "Local and remote numbers match, nothing needs to be done.")
+            Single.just(false)
+          } else {
+            Log.i(TAG, "Local (${TextSecurePreferences.getLocalNumber(this)}) and remote (${whoAmI.number}) numbers do not match, updating local.")
+            changeNumberRepository.changeLocalNumber(whoAmI.number)
+              .map { true }
+          }
+        }
+        .observeOn(AndroidSchedulers.mainThread())
+        .subscribeBy(onSuccess = { onChangeStatusConfirmed() }, onError = this::onFailedToGetChangeNumberStatus)
+    )
+  }
+
+  private fun onChangeStatusConfirmed() {
+    SignalStore.misc().unlockChangeNumber()
+
+    MaterialAlertDialogBuilder(this)
+      .setTitle(R.string.ChangeNumberLockActivity__change_status_confirmed)
+      .setMessage(getString(R.string.ChangeNumberLockActivity__your_number_has_been_confirmed_as_s, PhoneNumberFormatter.prettyPrint(TextSecurePreferences.getLocalNumber(this))))
+      .setPositiveButton(android.R.string.ok) { _, _ ->
+        startActivity(MainActivity.clearTop(this))
+        finish()
+      }
+      .setCancelable(false)
+      .show()
+  }
+
+  private fun onFailedToGetChangeNumberStatus(error: Throwable) {
+    Log.w(TAG, "Unable to determine status of change number", error)
+
+    MaterialAlertDialogBuilder(this)
+      .setTitle(R.string.ChangeNumberLockActivity__change_status_unconfirmed)
+      .setMessage(getString(R.string.ChangeNumberLockActivity__we_could_not_determine_the_status_of_your_change_number_request, error.javaClass.simpleName))
+      .setPositiveButton(R.string.ChangeNumberLockActivity__retry) { _, _ -> checkWhoAmI() }
+      .setNegativeButton(R.string.ChangeNumberLockActivity__leave) { _, _ -> finish() }
+      .setNeutralButton(R.string.ChangeNumberLockActivity__submit_debug_log) { _, _ ->
+        startActivity(Intent(this, SubmitDebugLogActivity::class.java))
+        finish()
+      }
+      .setCancelable(false)
+      .show()
+  }
+
+  companion object {
+    @JvmStatic
+    fun createIntent(context: Context): Intent {
+      return Intent(context, ChangeNumberLockActivity::class.java).apply {
+        flags = Intent.FLAG_ACTIVITY_SINGLE_TOP
+      }
+    }
+  }
+}
diff --git a/app/src/main/java/org/thoughtcrime/securesms/components/settings/app/changenumber/ChangeNumberRegistrationLockFragment.kt b/app/src/main/java/org/thoughtcrime/securesms/components/settings/app/changenumber/ChangeNumberRegistrationLockFragment.kt
index 16a078923f..a98e902269 100644
--- a/app/src/main/java/org/thoughtcrime/securesms/components/settings/app/changenumber/ChangeNumberRegistrationLockFragment.kt
+++ b/app/src/main/java/org/thoughtcrime/securesms/components/settings/app/changenumber/ChangeNumberRegistrationLockFragment.kt
@@ -2,6 +2,7 @@ package org.thoughtcrime.securesms.components.settings.app.changenumber
 
 import android.os.Bundle
 import android.view.View
+import androidx.activity.OnBackPressedCallback
 import androidx.appcompat.widget.Toolbar
 import androidx.navigation.fragment.findNavController
 import org.thoughtcrime.securesms.R
@@ -20,7 +21,16 @@ class ChangeNumberRegistrationLockFragment : BaseRegistrationLockFragment(R.layo
     super.onViewCreated(view, savedInstanceState)
 
     val toolbar: Toolbar = view.findViewById(R.id.toolbar)
-    toolbar.setNavigationOnClickListener { findNavController().navigateUp() }
+    toolbar.setNavigationOnClickListener { navigateUp() }
+
+    requireActivity().onBackPressedDispatcher.addCallback(
+      viewLifecycleOwner,
+      object : OnBackPressedCallback(true) {
+        override fun handleOnBackPressed() {
+          navigateUp()
+        }
+      }
+    )
   }
 
   override fun getViewModel(): BaseRegistrationViewModel {
@@ -60,4 +70,12 @@ class ChangeNumberRegistrationLockFragment : BaseRegistrationLockFragment(R.layo
       body
     )
   }
+
+  private fun navigateUp() {
+    if (SignalStore.misc().isChangeNumberLocked) {
+      startActivity(ChangeNumberLockActivity.createIntent(requireContext()))
+    } else {
+      findNavController().navigateUp()
+    }
+  }
 }
diff --git a/app/src/main/java/org/thoughtcrime/securesms/components/settings/app/changenumber/ChangeNumberRepository.kt b/app/src/main/java/org/thoughtcrime/securesms/components/settings/app/changenumber/ChangeNumberRepository.kt
index 0dd487a5ce..9fd581b2f5 100644
--- a/app/src/main/java/org/thoughtcrime/securesms/components/settings/app/changenumber/ChangeNumberRepository.kt
+++ b/app/src/main/java/org/thoughtcrime/securesms/components/settings/app/changenumber/ChangeNumberRepository.kt
@@ -18,6 +18,7 @@ import org.whispersystems.signalservice.api.KbsPinData
 import org.whispersystems.signalservice.api.KeyBackupSystemNoDataException
 import org.whispersystems.signalservice.internal.ServiceResponse
 import org.whispersystems.signalservice.internal.push.VerifyAccountResponse
+import org.whispersystems.signalservice.internal.push.WhoAmIResponse
 
 private val TAG: String = Log.tag(ChangeNumberRepository::class.java)
 
@@ -51,12 +52,18 @@ class ChangeNumberRepository(private val context: Context) {
     }.subscribeOn(Schedulers.io())
   }
 
+  @Suppress("UsePropertyAccessSyntax")
+  fun whoAmI(): Single<WhoAmIResponse> {
+    return Single.fromCallable { ApplicationDependencies.getSignalServiceAccountManager().getWhoAmI() }
+      .subscribeOn(Schedulers.io())
+  }
+
   @WorkerThread
   fun changeLocalNumber(e164: String): Single<Unit> {
-    TextSecurePreferences.setLocalNumber(context, e164)
-
     DatabaseFactory.getRecipientDatabase(context).updateSelfPhone(e164)
 
+    TextSecurePreferences.setLocalNumber(context, e164)
+
     ApplicationDependencies.closeConnections()
     ApplicationDependencies.getIncomingMessageObserver()
 
diff --git a/app/src/main/java/org/thoughtcrime/securesms/components/settings/app/changenumber/ChangeNumberViewModel.kt b/app/src/main/java/org/thoughtcrime/securesms/components/settings/app/changenumber/ChangeNumberViewModel.kt
index 205fe98e18..48b9d91a12 100644
--- a/app/src/main/java/org/thoughtcrime/securesms/components/settings/app/changenumber/ChangeNumberViewModel.kt
+++ b/app/src/main/java/org/thoughtcrime/securesms/components/settings/app/changenumber/ChangeNumberViewModel.kt
@@ -12,18 +12,21 @@ import com.google.i18n.phonenumbers.PhoneNumberUtil
 import io.reactivex.rxjava3.core.Single
 import org.signal.core.util.logging.Log
 import org.thoughtcrime.securesms.dependencies.ApplicationDependencies
+import org.thoughtcrime.securesms.keyvalue.SignalStore
 import org.thoughtcrime.securesms.pin.KbsRepository
 import org.thoughtcrime.securesms.pin.TokenData
 import org.thoughtcrime.securesms.registration.VerifyAccountRepository
 import org.thoughtcrime.securesms.registration.VerifyAccountResponseProcessor
 import org.thoughtcrime.securesms.registration.VerifyAccountResponseWithoutKbs
 import org.thoughtcrime.securesms.registration.VerifyCodeWithRegistrationLockResponseProcessor
+import org.thoughtcrime.securesms.registration.VerifyProcessor
 import org.thoughtcrime.securesms.registration.viewmodel.BaseRegistrationViewModel
 import org.thoughtcrime.securesms.registration.viewmodel.NumberViewState
 import org.thoughtcrime.securesms.util.DefaultValueLiveData
 import org.thoughtcrime.securesms.util.TextSecurePreferences
 import org.whispersystems.signalservice.internal.ServiceResponse
 import org.whispersystems.signalservice.internal.push.VerifyAccountResponse
+import java.util.Objects
 
 private val TAG: String = Log.tag(ChangeNumberViewModel::class.java)
 
@@ -104,6 +107,35 @@ class ChangeNumberViewModel(
     }
   }
 
+  override fun verifyCodeWithoutRegistrationLock(code: String): Single<VerifyAccountResponseProcessor> {
+    return super.verifyCodeWithoutRegistrationLock(code)
+      .doOnSubscribe { SignalStore.misc().lockChangeNumber() }
+      .flatMap(this::attemptToUnlockChangeNumber)
+  }
+
+  override fun verifyCodeAndRegisterAccountWithRegistrationLock(pin: String): Single<VerifyCodeWithRegistrationLockResponseProcessor> {
+    return super.verifyCodeAndRegisterAccountWithRegistrationLock(pin)
+      .doOnSubscribe { SignalStore.misc().lockChangeNumber() }
+      .flatMap(this::attemptToUnlockChangeNumber)
+  }
+
+  private fun <T : VerifyProcessor> attemptToUnlockChangeNumber(processor: T): Single<T> {
+    return if (processor.hasResult() || processor.isServerSentError()) {
+      SignalStore.misc().unlockChangeNumber()
+      Single.just(processor)
+    } else {
+      changeNumberRepository.whoAmI()
+        .map { whoAmI ->
+          if (Objects.equals(whoAmI.number, localNumber)) {
+            Log.i(TAG, "Local and remote numbers match, we can unlock.")
+            SignalStore.misc().unlockChangeNumber()
+          }
+          processor
+        }
+        .onErrorReturn { processor }
+    }
+  }
+
   override fun verifyAccountWithoutRegistrationLock(): Single<ServiceResponse<VerifyAccountResponse>> {
     return changeNumberRepository.changeNumber(textCodeEntered, number.e164Number)
   }
diff --git a/app/src/main/java/org/thoughtcrime/securesms/keyvalue/MiscellaneousValues.java b/app/src/main/java/org/thoughtcrime/securesms/keyvalue/MiscellaneousValues.java
index a9cc647138..c659b51b97 100644
--- a/app/src/main/java/org/thoughtcrime/securesms/keyvalue/MiscellaneousValues.java
+++ b/app/src/main/java/org/thoughtcrime/securesms/keyvalue/MiscellaneousValues.java
@@ -15,6 +15,7 @@ public final class MiscellaneousValues extends SignalStoreValues {
   private static final String CLIENT_DEPRECATED               = "misc.client_deprecated";
   private static final String OLD_DEVICE_TRANSFER_LOCKED      = "misc.old_device.transfer.locked";
   private static final String HAS_EVER_HAD_AN_AVATAR          = "misc.has.ever.had.an.avatar";
+  private static final String CHANGE_NUMBER_LOCK              = "misc.change_number.lock";
 
   MiscellaneousValues(@NonNull KeyValueStore store) {
     super(store);
@@ -97,4 +98,16 @@ public final class MiscellaneousValues extends SignalStoreValues {
   public void markHasEverHadAnAvatar() {
     putBoolean(HAS_EVER_HAD_AN_AVATAR, true);
   }
+
+  public boolean isChangeNumberLocked() {
+    return getBoolean(CHANGE_NUMBER_LOCK, false);
+  }
+
+  public void lockChangeNumber() {
+    putBoolean(CHANGE_NUMBER_LOCK, true);
+  }
+
+  public void unlockChangeNumber() {
+    putBoolean(CHANGE_NUMBER_LOCK, false);
+  }
 }
diff --git a/app/src/main/java/org/thoughtcrime/securesms/registration/VerifyAccountResponseProcessor.kt b/app/src/main/java/org/thoughtcrime/securesms/registration/VerifyAccountResponseProcessor.kt
index 3072e32adb..0cb9e669c0 100644
--- a/app/src/main/java/org/thoughtcrime/securesms/registration/VerifyAccountResponseProcessor.kt
+++ b/app/src/main/java/org/thoughtcrime/securesms/registration/VerifyAccountResponseProcessor.kt
@@ -1,6 +1,7 @@
 package org.thoughtcrime.securesms.registration
 
 import org.thoughtcrime.securesms.pin.TokenData
+import org.whispersystems.signalservice.api.push.exceptions.NonSuccessfulResponseCodeException
 import org.whispersystems.signalservice.internal.ServiceResponse
 import org.whispersystems.signalservice.internal.ServiceResponseProcessor
 import org.whispersystems.signalservice.internal.push.LockedException
@@ -9,7 +10,9 @@ import org.whispersystems.signalservice.internal.push.VerifyAccountResponse
 /**
  * Process responses from attempting to verify an account for use in account registration.
  */
-sealed class VerifyAccountResponseProcessor(response: ServiceResponse<VerifyAccountResponse>) : ServiceResponseProcessor<VerifyAccountResponse>(response) {
+sealed class VerifyAccountResponseProcessor(
+  response: ServiceResponse<VerifyAccountResponse>
+) : ServiceResponseProcessor<VerifyAccountResponse>(response), VerifyProcessor {
 
   open val tokenData: TokenData? = null
 
@@ -33,6 +36,10 @@ sealed class VerifyAccountResponseProcessor(response: ServiceResponse<VerifyAcco
     return error as LockedException
   }
 
+  override fun isServerSentError(): Boolean {
+    return error is NonSuccessfulResponseCodeException
+  }
+
   abstract fun isKbsLocked(): Boolean
 }
 
diff --git a/app/src/main/java/org/thoughtcrime/securesms/registration/VerifyCodeWithRegistrationLockResponseProcessor.kt b/app/src/main/java/org/thoughtcrime/securesms/registration/VerifyCodeWithRegistrationLockResponseProcessor.kt
index 9a1f2204fc..62d400690e 100644
--- a/app/src/main/java/org/thoughtcrime/securesms/registration/VerifyCodeWithRegistrationLockResponseProcessor.kt
+++ b/app/src/main/java/org/thoughtcrime/securesms/registration/VerifyCodeWithRegistrationLockResponseProcessor.kt
@@ -4,6 +4,7 @@ import org.thoughtcrime.securesms.pin.KeyBackupSystemWrongPinException
 import org.thoughtcrime.securesms.pin.TokenData
 import org.thoughtcrime.securesms.registration.VerifyAccountRepository.VerifyAccountWithRegistrationLockResponse
 import org.whispersystems.signalservice.api.KeyBackupSystemNoDataException
+import org.whispersystems.signalservice.api.push.exceptions.NonSuccessfulResponseCodeException
 import org.whispersystems.signalservice.internal.ServiceResponse
 import org.whispersystems.signalservice.internal.ServiceResponseProcessor
 import org.whispersystems.signalservice.internal.contacts.entities.TokenResponse
@@ -16,7 +17,7 @@ import org.whispersystems.signalservice.internal.push.VerifyAccountResponse
 class VerifyCodeWithRegistrationLockResponseProcessor(
   response: ServiceResponse<VerifyAccountWithRegistrationLockResponse>,
   val token: TokenData
-) : ServiceResponseProcessor<VerifyAccountWithRegistrationLockResponse>(response) {
+) : ServiceResponseProcessor<VerifyAccountWithRegistrationLockResponse>(response), VerifyProcessor {
 
   public override fun rateLimit(): Boolean {
     return super.rateLimit()
@@ -45,4 +46,10 @@ class VerifyCodeWithRegistrationLockResponseProcessor(
 
     return VerifyCodeWithRegistrationLockResponseProcessor(ServiceResponse.coerceError(response), token)
   }
+
+  override fun isServerSentError(): Boolean {
+    return error is NonSuccessfulResponseCodeException ||
+      error is KeyBackupSystemWrongPinException ||
+      error is KeyBackupSystemNoDataException
+  }
 }
diff --git a/app/src/main/java/org/thoughtcrime/securesms/registration/VerifyProcessor.kt b/app/src/main/java/org/thoughtcrime/securesms/registration/VerifyProcessor.kt
new file mode 100644
index 0000000000..ce09ec01cb
--- /dev/null
+++ b/app/src/main/java/org/thoughtcrime/securesms/registration/VerifyProcessor.kt
@@ -0,0 +1,6 @@
+package org.thoughtcrime.securesms.registration
+
+interface VerifyProcessor {
+  fun hasResult(): Boolean
+  fun isServerSentError(): Boolean
+}
diff --git a/app/src/main/res/layout/activity_change_number_lock.xml b/app/src/main/res/layout/activity_change_number_lock.xml
new file mode 100644
index 0000000000..21b02118af
--- /dev/null
+++ b/app/src/main/res/layout/activity_change_number_lock.xml
@@ -0,0 +1,77 @@
+<?xml version="1.0" encoding="utf-8"?>
+<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res-auto"
+    android:id="@+id/change_number_lock_scroll"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    android:clipToPadding="false"
+    android:fillViewport="true"
+    app:layout_constraintBottom_toBottomOf="parent"
+    app:layout_constraintEnd_toEndOf="parent"
+    app:layout_constraintStart_toStartOf="parent"
+    app:layout_constraintTop_toTopOf="parent">
+
+    <androidx.constraintlayout.widget.ConstraintLayout
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content">
+
+        <androidx.appcompat.widget.AppCompatImageView
+            android:id="@+id/change_number_lock_hero"
+            android:layout_width="64dp"
+            android:layout_height="64dp"
+            android:layout_marginTop="@dimen/transfer_top_padding"
+            app:layout_constraintBottom_toTopOf="@id/change_number_lock_header"
+            app:layout_constraintEnd_toEndOf="parent"
+            app:layout_constraintStart_toStartOf="parent"
+            app:layout_constraintTop_toTopOf="parent"
+            app:layout_constraintVertical_chainStyle="packed"
+            app:layout_constraintVertical_bias="0"
+            app:tint="@color/signal_alert_primary"
+            app:srcCompat="@drawable/ic_alert" />
+
+        <TextView
+            android:id="@+id/change_number_lock_header"
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:layout_marginStart="32dp"
+            android:layout_marginTop="@dimen/transfer_item_spacing"
+            android:layout_marginEnd="32dp"
+            android:gravity="center"
+            android:text="@string/AccountSettingsFragment__change_phone_number"
+            android:textAppearance="@style/TextAppearance.Signal.Title1"
+            app:layout_constraintBottom_toTopOf="@id/change_number_lock_body"
+            app:layout_constraintEnd_toEndOf="parent"
+            app:layout_constraintStart_toStartOf="parent"
+            app:layout_constraintTop_toBottomOf="@+id/change_number_lock_hero" />
+
+        <TextView
+            android:id="@+id/change_number_lock_body"
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:layout_marginStart="32dp"
+            android:layout_marginTop="12dp"
+            android:layout_marginEnd="32dp"
+            android:layout_marginBottom="32dp"
+            android:gravity="center_horizontal"
+            android:text="@string/ChangeNumberLockActivity__it_looks_like_you_tried_to_change_your_number_but_we_were_unable_to_determine_if_it_was_successful_rechecking_now"
+            android:textAppearance="@style/TextAppearance.Signal.Body1"
+            app:layout_constraintBottom_toBottomOf="parent"
+            app:layout_constraintEnd_toEndOf="parent"
+            app:layout_constraintStart_toStartOf="parent"
+            app:layout_constraintTop_toBottomOf="@+id/change_number_lock_header" />
+
+        <com.google.android.material.progressindicator.CircularProgressIndicator
+            android:id="@+id/change_phone_number_verify_progress"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:layout_marginTop="@dimen/transfer_top_padding"
+            android:indeterminate="true"
+            app:indicatorColor="@color/signal_accent_primary"
+            app:indicatorSize="48dp"
+            app:layout_constraintEnd_toEndOf="parent"
+            app:layout_constraintStart_toStartOf="parent"
+            app:layout_constraintTop_toBottomOf="@+id/change_number_lock_body" />
+
+    </androidx.constraintlayout.widget.ConstraintLayout>
+
+</ScrollView>
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index bbd02b0dd3..7855510ff5 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -3531,6 +3531,16 @@
     <string name="ChangeNumberPinDiffersFragment__update_pin">Update PIN</string>
     <string name="ChangeNumberPinDiffersFragment__keep_old_pin_question">Keep old pin?</string>
 
+    <!-- ChangeNumberLockActivity -->
+    <string name="ChangeNumberLockActivity__it_looks_like_you_tried_to_change_your_number_but_we_were_unable_to_determine_if_it_was_successful_rechecking_now">It looks like you tried to change your number but we were unable to determine if it was successful.\n\nRechecking now…</string>
+    <string name="ChangeNumberLockActivity__change_status_confirmed">Change status confirmed</string>
+    <string name="ChangeNumberLockActivity__your_number_has_been_confirmed_as_s">Your number has been confirmed as %1$s. If this is not your new number, please restart the change number process.</string>
+    <string name="ChangeNumberLockActivity__change_status_unconfirmed">Change status unconfirmed</string>
+    <string name="ChangeNumberLockActivity__we_could_not_determine_the_status_of_your_change_number_request">We could not determine the status of your change number request.\n\n(Error: %1$s)</string>
+    <string name="ChangeNumberLockActivity__retry">Retry</string>
+    <string name="ChangeNumberLockActivity__leave">Leave</string>
+    <string name="ChangeNumberLockActivity__submit_debug_log">Submit debug log</string>
+
     <!-- ChatsSettingsFragment -->
     <string name="ChatsSettingsFragment__keyboard">Keyboard</string>
     <string name="ChatsSettingsFragment__enter_key_sends">Enter key sends</string>
diff --git a/libsignal/service/src/main/java/org/whispersystems/signalservice/api/SignalServiceAccountManager.java b/libsignal/service/src/main/java/org/whispersystems/signalservice/api/SignalServiceAccountManager.java
index 2527b1cb1f..ddaceec66c 100644
--- a/libsignal/service/src/main/java/org/whispersystems/signalservice/api/SignalServiceAccountManager.java
+++ b/libsignal/service/src/main/java/org/whispersystems/signalservice/api/SignalServiceAccountManager.java
@@ -65,6 +65,7 @@ import org.whispersystems.signalservice.internal.push.RemoteConfigResponse;
 import org.whispersystems.signalservice.internal.push.RequestVerificationCodeResponse;
 import org.whispersystems.signalservice.internal.push.SignalServiceProtos;
 import org.whispersystems.signalservice.internal.push.VerifyAccountResponse;
+import org.whispersystems.signalservice.internal.push.WhoAmIResponse;
 import org.whispersystems.signalservice.internal.push.http.ProfileCipherOutputStreamFactory;
 import org.whispersystems.signalservice.internal.storage.protos.ManifestRecord;
 import org.whispersystems.signalservice.internal.storage.protos.ReadOperation;
@@ -169,6 +170,10 @@ public class SignalServiceAccountManager {
     return this.pushServiceSocket.getOwnUuid();
   }
 
+  public WhoAmIResponse getWhoAmI() throws IOException {
+    return this.pushServiceSocket.getWhoAmI();
+  }
+
   public KeyBackupService getKeyBackupService(KeyStore iasKeyStore,
                                               String enclaveName,
                                               byte[] serviceId,
diff --git a/libsignal/service/src/main/java/org/whispersystems/signalservice/internal/push/PushServiceSocket.java b/libsignal/service/src/main/java/org/whispersystems/signalservice/internal/push/PushServiceSocket.java
index bce80d5540..acfcee9dea 100644
--- a/libsignal/service/src/main/java/org/whispersystems/signalservice/internal/push/PushServiceSocket.java
+++ b/libsignal/service/src/main/java/org/whispersystems/signalservice/internal/push/PushServiceSocket.java
@@ -328,6 +328,10 @@ public class PushServiceSocket {
     }
   }
 
+  public WhoAmIResponse getWhoAmI() throws IOException {
+    return JsonUtil.fromJson(makeServiceRequest(WHO_AM_I, "GET", null), WhoAmIResponse.class);
+  }
+
   public VerifyAccountResponse verifyAccountCode(String verificationCode, String signalingKey, int registrationId, boolean fetchesMessages,
                                                  String pin, String registrationLock,
                                                  byte[] unidentifiedAccessKey, boolean unrestrictedUnidentifiedAccess,
diff --git a/libsignal/service/src/main/java/org/whispersystems/signalservice/internal/push/WhoAmIResponse.java b/libsignal/service/src/main/java/org/whispersystems/signalservice/internal/push/WhoAmIResponse.java
index 6d50117f7f..8ca14e141e 100644
--- a/libsignal/service/src/main/java/org/whispersystems/signalservice/internal/push/WhoAmIResponse.java
+++ b/libsignal/service/src/main/java/org/whispersystems/signalservice/internal/push/WhoAmIResponse.java
@@ -6,7 +6,14 @@ public class WhoAmIResponse {
   @JsonProperty
   private String uuid;
 
+  @JsonProperty
+  private String number;
+
   public String getUuid() {
     return uuid;
   }
+
+  public String getNumber() {
+    return number;
+  }
 }