FRITZ!App Fon Service - Knowledge Base

FRITZ!App Fon Service

FRITZ!App Fon reports "Could not start VoIP telephony"

FRITZ!App Fon cannot be opened. When you attempt to start FRITZ!App Fon, the error message "Could not start VoIP telephony. Make sure that no other VoIP applications are active and try again" is displayed.


  • VoLTE (Voice over LTE) is enabled on the iPhone and it uses the same port as FRITZ!App Fon.

1 Wait for upcoming FRITZ!App version

VoLTE and FRITZ!App Fon both use port 5060 to communicate. When port 5060 is being used by VoLTE, then FRITZ!App Fon cannot use it.

We are currently investigating whether we can make a new version of FRITZ!App Fon available that would allow the simultaneous use of FRITZ!App Fon and VoLTE. If a solution is possible, we shall make a corresponding update available for FRITZ!App Fon. You can always check the Apple App Store to see whether an update is available.


If you disable VoLTE, then you can use FRITZ!App Fon:

  1. Open the iOS settings.
  2. Tap "Cellular" and then "Enable LTE".
  3. Tap "Data Only" to disable VoLTE.