So I have a bit of a difficult situation. I did a small install in an office with only one phone line at first. As a hardware phone we opted for a Yealink W60b Base with a W56H Handset. The setup is just working fine with no issues.

A couple months later the customer got a second line from the provider (German Telekom) which we setup in freePBX and got the customer a Yealink W52H as a mobile device. Strangely this phone is making and receiving calls just fine but if it gets called from outside the caller isn’t able to hear anything while the receiver is hearing anything normal. Also the call gets ended after around 30 seconds ago. I tried switching the lines around so the “old” line would lead to the new handset and vice versa and now the problem moved to the old line. So I thought it must be the handset. But both are configured the same (nearly defaults) and also the problem doesn’t exist internal calls.

Has anyone got an idea what the problem could be?