Ok, I'm really stumped by this one. I'm attempting to configure 3CX in it's demo form to show that it works and performs the tasks required of it. Unfortunately, every time I place an incoming call, it connects, shows on the phone's called ID, and might even get around to ringing, but then the call gets terminated. So far, I've tried fiddling with the STUN and port settings (both on the PBX and router, eventually returning to defaults), and checking through the logs for details. Further Information: Message received by the incoming phone (the one attempting to call the PBX) is "User Busy". The logs for the calls are: Code: 14:19:50.406 [CM503008]: Call(3): Call is terminated 14:19:50.265 [CM505001]: Ext.204: Device info: Device Not Identified: User Agent not matched; Capabilities:[reinvite, replaces, able-no-sdp, recvonly] UserAgent: [sipagent MAC:00-50-7F-39-3E-14 V:12202.26.1.03i-SIP] PBX contact: [sip:email@example.com:5060] 14:19:50.265 [CM503002]: Call(3): Alerting sip:firstname.lastname@example.org:5060 14:19:50.093 [CM503025]: Call(3): Calling Ext:Ext.204@[Dev:sip:email@example.com:5060] 14:19:50.093 [MS210002] C:3.2:Offer provided. Connection(transcoding mode): 192.168.1.27:7004(7005) 14:19:50.078 [CM503004]: Call(3): Route 1: Ext:Ext.204@[Dev:sip:firstname.lastname@example.org:5060] 14:19:50.078 [CM503010]: Making route(s) to <sip:email@example.com:5060> 14:19:50.078 [MS210000] C:3.1:Offer received. RTP connection: 220.127.116.11:55294(55295) 14:19:50.062 Remote SDP is set for legC:3.1 14:19:50.062 [CM505003]: Provider:[Draytel] Device info: Device Not Identified: User Agent not matched; Capabilities:[reinvite, replaces, able-no-sdp, recvonly] UserAgent: [Asterisk PBX] PBX contact: [sip:firstname.lastname@example.org:5060] 14:19:50.062 [CM503001]: Call(3): Incoming call from 07920585714@(Ln.10000@Draytel) to <sip:email@example.com:5060> 14:19:50.031 [CM503012]: Inbound out-of-office hours rule (604) for 10000 forwards to DN:204 14:19:50.031 Looking for inbound target: called=IBT-8249258-01205805604; caller=07920585714 14:19:50.031 [CM500002]: Info on incoming INVITE: INVITE sip:firstname.lastname@example.org:5060;rinstance=e260a5455c9ca78d SIP/2.0 Via: SIP/2.0/UDP 18.104.22.168:5065;branch=z9hG4bK57be.61916274.0 Via: SIP/2.0/UDP 22.214.171.124;branch=z9hG4bK57be.73cfc1f7.1 Via: SIP/2.0/UDP 126.96.36.199;branch=z9hG4bK57be.63cfc1f7.0 Via: SIP/2.0/UDP 188.8.131.52:5061;received=184.108.40.206;branch=z9hG4bK68e9dd20;rport=5061 Max-Forwards: 67 Record-Route: <sip:email@example.com:5065;lr=on;ftag=as257f6166> Record-Route: <sip:220.127.116.11;r2=on;lr=on;ftag=as257f6166> Record-Route: <sip:18.104.22.168;r2=on;lr=on;ftag=as257f6166> Record-Route: <sip:22.214.171.124;lr=on;ftag=as257f6166> Contact: <sip:firstname.lastname@example.org:5061> To: <sip:IBTemail@example.com> From: "07920585714"<sip:firstname.lastname@example.org:5061>;tag=as257f6166 Call-ID: email@example.com CSeq: 102 INVITE Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY Date: Mon, 28 Jun 2010 13:20:00 GMT Supported: replaces User-Agent: Asterisk PBX Content-Length: 0 P-hint: inbound IBT, call to user P-RTP-Proxy: Yes Does anyone have any idea where to go from here? Any help is appreciated.