I am using the native internet calling feature provided on Jelly Bean. (I believe this feature has been available since Gingerbread.) I can make outgoing calls without issue. Since my SIP account is connected to a PSTN (i.e. phone number) I can also receive calls. However, when I answer an incoming call the calling party can hear me, but I cannot hear the caller on the other end.
My guess is that this is some kind of NAT problem. See here, for example. With other third-party SIP apps it is possible to use STUN to eliminate the problem. I don't see any corresponding options for the native SIP interface, though. So I have two related questions:
1. Is it possible to enable/use STUN with native internet calling?
2. How can I troubleshoot problems with native internet calling?