Fritz Fon app on iPhone - incoming DV call, can't hear/speak

Hi everyone - I think this forum is the most suitable to post my question.

When we receive an incoming call on our landline, the DECT phones ring (as they should) and my iPhone rings too (I have set it to use the 'Frrritz' ring so I know that it's the house phone).

If I answer on any of the DECT phones, no problem. But if I try to answer on my iPhone, the general ring stops (so I think that the Fritzbox and the DECT phones have detected that I have picked up the call) but I can't hear the caller and the caller can't hear me.

This is our setup: Fritzbox 7530, iPhone Fritz Fon app and Panasonic DECT base station plugged into FON port (several Panason DECT phones around the house, all from the same kit).

TBH, we get very few calls on our landline so it's not a major issue. It's more that I am likely to have my iPhone on me if, for example, I am in the garden and it would be convenient to be able to answer calls to the house phone.

It's been a while since I've posted, so long that I had to register afresh - looking back in my low-tech password manager (card index), I registered originally on adslguide in late 2002!

Thanks in advance for any pointers

I had similar problems with the FritzApp and a 7590 and in the end gave up using the App (DECT phones are working fine).
If you want to troubleshoot, start with getting the most recent FRITZ!OS installed, 7.57 is the latest version for the 7530. If you have a 7530AX, then it is 7.80. But the box will tell you anyway when you use the Fritzbox Update Wizard.
The most recent version of the Fon App appears to be 2.12.0

If none of it works, I would raise a support case with AVM, they are normally quite good with their respomses

The Fritz! Fon app on my iPhone is version 5.4.1

What happens if you call out via the Fritz app, can you call another number and hear/be heard?

I checked the Fritz OS on the 7530 by running the update wizard - it is 7.57 (installed on 17.05.2024). I've also checked the Fritz Fon on my iPhone - it is 5.4.1 (from the settings/about Fritz!App Fon in the app itself) - I can't tell when that update happened. I do keep the iOS on my iPhone up to date - in between my original post and now, I have updated the iOS from 17.4.1 to the latest one 17.5.

Thanks also for the suggestion to try dialing out. I tried a test call using the app on my iPhone - the other person's phone rings OK and I can hear it ringing on my iPhone too but, when they answer, neither of us can hear the other.

When I have a bit more time, I will look to raise a case with AVM and see what they say.

Thank you to all of you for your comments/suggestions - it's great to be able to talk this through with you.

On the face of it, call signalling working but call media silence sounds like the symptoms of if an incompatible voice codec was selected. but I thought G.711 was automatically configured.

Hopefully it is not a NAT problem for which this was another classic symptom.
But should not be the case when the Fritz!box is directly on the Internet connection since it has a public IP and will in effect be its own session border for the call, rather than relying on an upstream router to source-NAT the outgoing voice packets.

Which ISP is it?

I don't think either poster has said unless elsewhere; my setup with a single DECT works fine and not tried the app,
but i suppose it depends whether that sends voice through the router's SIP or tries to setup a direct connection for the RTP media.

I rather assumed the app is only intended to work on the same LAN via Wi-Fi abd don't know if it has a different mode for outside the home.