I can make outgoing calls OK (using DID-Logic and the Nokia VOIP function) but incoming calls stop working after a few minutes.
It has been suggested the SIP Session Interval setting should be changed from 1800 to 0 but this value seems to do nothing. I tried 0, 60, 300, 600, 3600. None of them have any effect.
SIP is supposed to have a keep-alive timer but it doesn't seem to be functional. This has two issues: the SIP provider may drop the session, and definitely the WIFI router's NAT will close the mapping so the incoming call won't get through.
There is stuff all over the net (google) and I suspect this is a bug in Nokia's VOIP. The keep-alive feature doesn't do anything.
There is another setting called Registration, with options of
which also doesn't do anything whatsoever. If I set Always ON, and come back after a while, I find it has changed back to When Needed. But even if I leave the phone in that menu, and keep it on Always On, the incoming calls still cannot get through after the first few minutes starting from the initial (manual) login to the SIP provider.