Phone: MyTouch 4G Android 2.2.1 3CX 1.3.1 PBX: Grandstream 5024 (behind D-Link DIR-655) Using External Server 3G Enabled I've got my MyTouch registered to my PBX. I've got one profile set for when I'm internal to my network. It seems to work fine. I've got a 2d profile for when I've outside. I've got it pointing to my public IP address. The phone registers fine. When I place or receive a call I get no audio on either end of the call. I've got a similar issue with SIP Droid. Is this a NAT issue. If so, how do I deal with it? BTW: I'm on T-Mobile. I'm now wondering whether they block SIP. If that is the case is there a work-around (e.g. VPN of some sort?).