I have the app working on our internal network. Works great. Everyone in my office wants to know when it's going live I tried it on ATT 3G. It can connect to the 3CX server, registers correctly, everything appears to work, but no audio on calls. I tried it at Starbucks on wifi and everything including audio works correctly. I also tried it from home and a few other places with wifi and it worked correctly. So it appears ATT is blocking SIP. One other issue is the contact lookup. It looks up contacts correctly, but crashes when I select one to dial. I'm syncing with Exchange Active Sync. Iphone 4 running 4.1 without jailbreak.