Trying to get my first 3CX PBX working and just got off the phone with a very capable tech support guy from my trunk provider. He was able to get everything almost working, but calls were dropping after 20 or 30 seconds since (in his words) " the CONTACT header contains port :3200 and the provider is responding back with an ACK to what ever is in the contact header." The following are lines he thought relevant from the 3CX log: Contact: <sip:firstname.lastname@example.org:3200 [CM505003]: Provider:[Nexvortex - US] Device info: Device Not Identified: User Agent not matched; Capabilities:[reinvite, replaces, able-no-sdp, recvonly] UserAgent:  PBX contact: [sip:Ow11223Rbxn@184.108.40.206:3200] He also mentioned that it is not my router causing the problem because he was able to go into 3CX and explicitly make it use port 5060 and that it was being changed to 3200 within the 3CX PBX. He was not able to figure out how this was happening or where to change it and told me that it was a question for 3CX. Anybody have any ideas? Thanks!