I am running MCD 4.2 SP2 that has a ThinkTel SIP trunk using a MBG for a sip Proxy. The SIP Peer profile options are taken from the ThinkTel SIP COE document.
When dialing out we get dead air, packet captures show the PBX is not sending an INVITE to the MBG to start setting up a call. CCS Trace shows the call is using my SIP trunk.