(Hi guys! Going for certification I have a iphone 3gs with ATT. Current setup, 2008 domain server R2 running exchange UM and 3cx on a Windows 7 box (behind Cisco E2000). Tried opening ALL listed ports (5060, 5090, 9000-10000, etc) and more on technical docs for 3cx. The only solution to get the iphone to register is to put it in the DMZ?! Seems that some ports are missing (Any ideas?). As soon as I pop the 3cx in the dmz, it registers. So I know it is not the server or firewall on windows. Working fine, accepting calls and outbound calls internally. However when I download the 3cx app and run it on the iphone, it will register, say it is online, and will call out and ring to extensions, operator, outside numbers, etc. BUT it will have no audio both ways. Any idea? I have read all documentation and setup as best as I know how to. My config is as follows. 3cx sitting on dmz for testing. Internal: 10.0.0.10 Ext: My private IP (pointing to my 10.0.0.0 net) STUN: stun3.3cx.com No changes in codecs. This what happens when I register, and call an my operator extension..... 14:11:38.553 Currently active calls - 1:  14:11:12.205 [CM503007]: Call(23): Device joined: sip:email@example.com:5060;transport=TCP 14:11:12.202 [CM503007]: Call(23): Device joined: sip:firstname.lastname@example.org:12285 14:11:12.190 [CM503002]: Call(23): Alerting sip:10.0.0.2:5060;transport=TCP 14:11:11.018 [CM503025]: Call(23): Calling @[Dev:sip:10.0.0.2:5060;transport=TCP] 14:11:11.008 [CM503004]: Call(23): Route 1: @[Dev:sip:10.0.0.2:5060;transport=TCP] 14:11:11.007 [CM503010]: Making route(s) to <sip:email@example.com> 14:11:11.001 [CM505001]: Ext.1001: Device info: Device Not Identified: User Agent not matched; Capabilities:[reinvite, replaces, able-no-sdp, recvonly] UserAgent: [3CXPhone for iPhone 1.0.19] PBX contact: [sip:firstname.lastname@example.org:5060] 14:11:10.993 [CM503001]: Call(23): Incoming call from Ext.1001 to <sip:email@example.com> And just dead air, rings like once.