I'm trying to get a Callcentric SIP trunk to work with 3CX, but am having some problems. The 3CX server is inside my network and communicates through a Forefront TMG server out to the internet. I've installed the 3CX softphone on the PBX server and configured it for my Callcentric account and I am able to successfully make outbound calls and receive incoming calls, so the TMG firewall seems to be passing traffic okay. I used the Callcentric template when adding the VoIP provider, and I can successfully receive incoming calls. However, when I dial an outbound call, I see this in the logs: Code: 26-08-2012 14:31:59.524 Leg L:18.1[Extn] is terminated: Cause: 200 BYE from PBX 26-08-2012 14:31:59.472 Leg L:18.2[Line:10000>>CCNACCOUNTNUMBER] is terminated: Cause: 408 Request Timeout/INVITE from local 26-08-2012 14:31:59.470 [CM503020]: Call(C:18): Normal call termination. Call originator: Extn:15. Reason: No answer 26-08-2012 14:31:59.470 [CM503016]: Call(C:18): Attempt to reach <sip:5OUTBOUNDNUMBER@PBXINTERNALIP:5060> from Extn:15 has failed. Reason: No Answer 26-08-2012 14:31:59.469 [CM503003]: Call(C:18): Call to <sip:OUTBOUNDNUMBER@callcentric.com:5060> has failed; Cause: 408 Request Timeout/INVITE from local 26-08-2012 14:31:38.590 Currently active calls - 1:  26-08-2012 14:31:27.351 [CM503025]: Call(C:18): Calling T:Line:10000>>OUTBOUNDNUMBER@[Dev:sip:CCNACCOUNTNUMBER@callcentric.com:5060] 26-08-2012 14:31:27.298 [CM503027]: Call(C:18): From: Extn:15 ("15" <sip:15@PBXINTERNALIP:5060>) to T:Line:10000>>OUTBOUNDNUMBER@[Dev:sip:CCNACCOUNTNUMBER@callcentric.com:5060] 26-08-2012 14:31:27.298 [CM503004]: Call(C:18): Route 1: T:Line:10000>>OUTBOUNDNUMBER@[Dev:sip:CCNACCOUNTNUMBER@callcentric.com:5060] 26-08-2012 14:31:27.297 [CM503001]: Call(C:18): Incoming call from Extn:15 to <sip:5OUTBOUNDNUMBER@172.20.0.4:5060> The outbound rule is set that prefix 5 dials via the VoIP provider and strips the 5, and I am dialing an 11 digit US phone number (which works fine when testing with the 3CX softphone). Are there any suggestions where I might look to start debugging this?