I've already opened a case with 3CX, but I figured I'd post it here just in case the community could provide some insight. So here's what going on - we are not getting any audio on the phones (inbound, outbound, ext to ext). However, I have tested a successful call from the 3CX client on a Mac. Here are the details: We are using 3CX V15. SIP Provider: CallCentric We have forwarded all the necessary ports and the Firewall Check passes. We have provisioned a Yealink T46G, Grandstream GXP2140 and GXP2130 to the system and they are able to send and receive a call, but there is no audio. When we check the CallCentric call reports we see the calls being logged. These phones are configured using the "Direct SIP (STUN remote)" Provisioning Method since they will be remote extensions outside of the data center. Not that it matters, but I uploaded a screenshot of my Dashboard. The four extensions are the IP phones (1x Yealink T46G, 2x Grandstream GXP2140 and 1x GXP2130). The fifth extension is the 3CX Client (Mac, currently offline).