Has anyone ran into a similar problem with a Cisco 7960? If I make a call from the 7960 phone to an external number, the call will continue for however long it's needed. If I make an internal call with the 7960 phone to VM or another extension the call only makes it to 32 seconds, and the 3CX PBX sends a BYE. I traced it down with Wireshark and it looks like the 7960 fails to send an ACK after the PBX sends the 200 OK. The PBX continues to re-try until a timer expires I guess and then the BYE gets sent. The call appears to be setup correctly with audio both ways, but for some reason the 7960 doesn't send the last ACK. I did some searching on the web and found a solution for the exact problem on a FreePBX site. Apparently there's a function in FreePBX that you can disable called "strict SIP processing" that fixed the problem on the FreePBX setup. Is there such an option with 3CX? I have a VPN link from an office internal network to a hosted server running the 3CX app for the Cisco phones. I did that cause they wouldn't register with an external IP, but that's another story.