Handset intermittent connectivity

[ThanasisPolitis]

We have a Yealink T23G handset that is playing up...
It receives calls intermittently and some times it shows as "Service Unavailable"
On the server, it comes up 3 times under the same extension!
The phone is STUN provisioned.
We have tried to remove it from the extension and also reset it to factory defaults.
It still does the same thing... Any ideas?

 

[StefanW]

when this is a STUN phone and I see a local IP address, then I have a feeling there is SIP ALG in the firewall.

My advice, for a single device at home --> 3CX mobile apps or webclient... Both work with the tunnel around such firewall issues...