diff --git a/PRIVACY.md b/PRIVACY.md
index 6ed3eae..9071878 100644
--- a/PRIVACY.md
+++ b/PRIVACY.md
@@ -9,4 +9,9 @@ please read them at:
 
 Signal: https://signal.org/legal/#privacy-policy  
 Telegram: https://telegram.org/privacy  
-Threema: https://threema.ch/privacy_policy/  
+Threema: https://threema.ch/privacy_policy/
+
+Fallback services:
+
+WhatsApp: https://www.whatsapp.com/privacy
+Viber: https://www.viber.com/en/terms/viber-privacy-policy/
diff --git a/app/build.gradle b/app/build.gradle
index 3643d4d..6991672 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -10,8 +10,8 @@ android {
         applicationId "me.lucky.red"
         minSdk 29
         targetSdk 32
-        versionCode 6
-        versionName "1.0.5"
+        versionCode 7
+        versionName "1.0.6"
 
         testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
     }
diff --git a/app/src/main/java/me/lucky/red/CallRedirectionService.kt b/app/src/main/java/me/lucky/red/CallRedirectionService.kt
index 37a0448..8584237 100644
--- a/app/src/main/java/me/lucky/red/CallRedirectionService.kt
+++ b/app/src/main/java/me/lucky/red/CallRedirectionService.kt
@@ -15,10 +15,18 @@ class CallRedirectionService : CallRedirectionService() {
         private const val SIGNAL_MIMETYPE = "$PREFIX.org.thoughtcrime.securesms.call"
         private const val TELEGRAM_MIMETYPE = "$PREFIX.org.telegram.messenger.android.call"
         private const val THREEMA_MIMETYPE = "$PREFIX.ch.threema.app.call"
+        private const val WHATSAPP_MIMETYPE = "$PREFIX.com.whatsapp.voip.call"
+        private const val VIBER_MIMETYPE = "$PREFIX.com.viber.voip.call"
         private val MIMETYPES = mapOf(
             SIGNAL_MIMETYPE to 0,
             TELEGRAM_MIMETYPE to 1,
             THREEMA_MIMETYPE to 2,
+            WHATSAPP_MIMETYPE to 48,
+            VIBER_MIMETYPE to 49,
+        )
+        private val FALLBACK_MIMETYPES = arrayOf(
+            WHATSAPP_MIMETYPE,
+            VIBER_MIMETYPE,
         )
     }
 
@@ -59,7 +67,7 @@ class CallRedirectionService : CallRedirectionService() {
             return
         }
         val record = records.minByOrNull { MIMETYPES[it.mimetype] ?: 0 }
-        if (record == null) {
+        if (record == null || (record.mimetype in FALLBACK_MIMETYPES && !prefs.isFallbackChecked)) {
             placeCallUnmodified()
             return
         }
@@ -67,6 +75,8 @@ class CallRedirectionService : CallRedirectionService() {
             SIGNAL_MIMETYPE -> R.string.destination_signal
             TELEGRAM_MIMETYPE -> R.string.destination_telegram
             THREEMA_MIMETYPE -> R.string.destination_threema
+            WHATSAPP_MIMETYPE -> R.string.fallback_destination_whatsapp
+            VIBER_MIMETYPE -> R.string.fallback_destination_viber
             else -> return
         })
     }
diff --git a/app/src/main/java/me/lucky/red/MainActivity.kt b/app/src/main/java/me/lucky/red/MainActivity.kt
index 14f1564..c9e3fd3 100644
--- a/app/src/main/java/me/lucky/red/MainActivity.kt
+++ b/app/src/main/java/me/lucky/red/MainActivity.kt
@@ -48,6 +48,7 @@ class MainActivity : AppCompatActivity() {
         binding.apply {
             redirectionDelay.value = (prefs.redirectionDelay / 1000).toFloat()
             popupPosition.editText?.setText(prefs.popupPosition.toString())
+            fallback.isChecked = prefs.isFallbackChecked
             toggle.isChecked = prefs.isServiceEnabled
         }
     }
@@ -65,6 +66,9 @@ class MainActivity : AppCompatActivity() {
                     prefs.popupPosition = it?.toString()?.toInt() ?: return@doAfterTextChanged
                 } catch (exc: NumberFormatException) {}
             }
+            fallback.setOnCheckedChangeListener { _, isChecked ->
+                prefs.isFallbackChecked = isChecked
+            }
             toggle.setOnCheckedChangeListener { _, isChecked ->
                 if (isChecked && !hasPermissions()) {
                     toggle.isChecked = false
diff --git a/app/src/main/java/me/lucky/red/Preferences.kt b/app/src/main/java/me/lucky/red/Preferences.kt
index e75288e..33b11b1 100644
--- a/app/src/main/java/me/lucky/red/Preferences.kt
+++ b/app/src/main/java/me/lucky/red/Preferences.kt
@@ -9,6 +9,10 @@ class Preferences(ctx: Context) {
         private const val SERVICE_ENABLED = "service_enabled"
         private const val REDIRECTION_DELAY = "redirection_delay"
         private const val POPUP_POSITION = "popup_position_y"
+        private const val FALLBACK_CHECKED = "fallback_checked"
+
+        private const val DEFAULT_REDIRECTION_DELAY = 2000L
+        private const val DEFAULT_POPUP_POSITION = 333
     }
 
     private val prefs = PreferenceManager.getDefaultSharedPreferences(ctx)
@@ -18,10 +22,14 @@ class Preferences(ctx: Context) {
         set(value) = prefs.edit { putBoolean(SERVICE_ENABLED, value) }
 
     var redirectionDelay: Long
-        get() = prefs.getLong(REDIRECTION_DELAY, 2000L)
+        get() = prefs.getLong(REDIRECTION_DELAY, DEFAULT_REDIRECTION_DELAY)
         set(value) = prefs.edit { putLong(REDIRECTION_DELAY, value) }
 
     var popupPosition: Int
-        get() = prefs.getInt(POPUP_POSITION, 333)
+        get() = prefs.getInt(POPUP_POSITION, DEFAULT_POPUP_POSITION)
         set(value) = prefs.edit { putInt(POPUP_POSITION, value) }
+
+    var isFallbackChecked: Boolean
+        get() = prefs.getBoolean(FALLBACK_CHECKED, false)
+        set(value) = prefs.edit { putBoolean(FALLBACK_CHECKED, value) }
 }
diff --git a/app/src/main/res/layout/activity_main.xml b/app/src/main/res/layout/activity_main.xml
index b24c9e1..3753d2f 100644
--- a/app/src/main/res/layout/activity_main.xml
+++ b/app/src/main/res/layout/activity_main.xml
@@ -20,6 +20,7 @@
         android:id="@+id/scrollView"
         android:layout_width="0dp"
         android:layout_height="0dp"
+        android:padding="16dp"
         android:layout_marginVertical="16dp"
         app:layout_constraintBottom_toTopOf="@+id/toggle"
         app:layout_constraintEnd_toEndOf="parent"
@@ -42,6 +43,7 @@
 
             <TextView
                 android:id="@+id/description2"
+                android:textSize="12sp"
                 android:layout_width="match_parent"
                 android:layout_height="wrap_content"
                 android:text="@string/redirection_delay_description" />
@@ -64,6 +66,33 @@
 
             </com.google.android.material.textfield.TextInputLayout>
 
+            <Space
+                android:layout_marginVertical="8dp"
+                android:layout_width="match_parent"
+                android:layout_height="wrap_content" />
+
+            <View
+                android:id="@+id/divider"
+                android:layout_width="match_parent"
+                android:layout_height="1dp"
+                android:layout_marginVertical="8dp"
+                android:background="?android:attr/listDivider" />
+
+            <CheckBox
+                android:id="@+id/fallback"
+                android:layout_width="match_parent"
+                android:layout_height="wrap_content"
+                android:layoutDirection="rtl"
+                android:text="@string/fallback"
+                android:textSize="16sp" />
+
+            <TextView
+                android:id="@+id/description3"
+                android:layout_width="match_parent"
+                android:layout_height="wrap_content"
+                android:text="@string/fallback_description"
+                android:textSize="12sp" />
+
         </LinearLayout>
     </ScrollView>
 
diff --git a/app/src/main/res/values-ru/strings.xml b/app/src/main/res/values-ru/strings.xml
index 1008539..d130df9 100644
--- a/app/src/main/res/values-ru/strings.xml
+++ b/app/src/main/res/values-ru/strings.xml
@@ -8,4 +8,8 @@
     <string name="destination_threema">Threema</string>
     <string name="redirection_delay_description">Задержка до того, как звонок будет перенаправлен.</string>
     <string name="popup_position">Позиция всплывающего окна</string>
+    <string name="fallback">Обратная совместимость</string>
+    <string name="fallback_description">Перенаправлять в WhatsApp/Viber, если другие недоступны.</string>
+    <string name="fallback_destination_whatsapp">WhatsApp</string>
+    <string name="fallback_destination_viber">Viber</string>
 </resources>
\ No newline at end of file
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index bb96707..ed314bc 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -8,4 +8,8 @@
     <string name="destination_threema">Threema</string>
     <string name="redirection_delay_description">Delay before a call will be redirected.</string>
     <string name="popup_position">Popup position</string>
+    <string name="fallback">Fallback</string>
+    <string name="fallback_description">Redirect to WhatsApp/Viber if no other available.</string>
+    <string name="fallback_destination_whatsapp">WhatsApp</string>
+    <string name="fallback_destination_viber">Viber</string>
 </resources>
\ No newline at end of file
diff --git a/fastlane/metadata/android/en-US/changelogs/7.txt b/fastlane/metadata/android/en-US/changelogs/7.txt
new file mode 100644
index 0000000..ef26257
--- /dev/null
+++ b/fastlane/metadata/android/en-US/changelogs/7.txt
@@ -0,0 +1 @@
+fallback mode
diff --git a/fastlane/metadata/android/en-US/images/phoneScreenshots/1.png b/fastlane/metadata/android/en-US/images/phoneScreenshots/1.png
index fba57b5..a4f81f7 100644
Binary files a/fastlane/metadata/android/en-US/images/phoneScreenshots/1.png and b/fastlane/metadata/android/en-US/images/phoneScreenshots/1.png differ