With my Asterisk box DMZ'd (for testing only - not full time!!) I can use IDEFISK IAX softphone over my laptop with Sierra card, and everything works great (call quality and latency is acceptable, but not perfect).
If I use any SIP softphone, I can connect to the PBX just fine, and make/recieve calls, and hear ringing tone, but there is no actual call audio either way once connected.
Anyone else had similar problems? I initially thought it was port issues, but I thought DMZ would remove that as an issue?