Dear Members, I'm new in this community and I have immediate a question. Hope somebody finds an answer. I installed the 3CX on my iphone. After 2 h of setting and tweaking with all of the SIP Server Setting and so on I finally get the phone running. works pretty well -only in WLAN- Now to my question. I get contact only if I'm in the WLAN. If I use the 3G connection of AT&T here in the US I get no connection. 3CX logs in and get connected but if I try to do a call no connection. Are there any specifc settings necessary or does AT&T not allow to do VOIP. T-Mobile however doesn't let me in at all.... Thanks for answers Greetings J.