The more interesting question is why the reinvite is being rejected:
Status-Line: SIP/2.0 400 Bad Request Message Header Via: SIP/2.0/UDP [PUBLIC-MITEL]:5060;received=[PUBLIC-MITEL];branch=z9hG4bK-d8754z-2648756d6bb46b65-1---d8754z-;rport=5060 From: sip:pstn-did@[PUBLIC-MITEL]:5060;tag=0_1970073968-102972850 To: sip:+1callerid-did@[PSTN-IPADDRESS]:5060;tag=gK0e4a212a Call-ID: 1309573957_105226997@[PSTN-IPADDRESS] CSeq: 747722615 INVITE Error-Info: sip:+1callerid-did@[PSTN-IPADDRESS];cause="[line 007] SIP syntax error" Content-Length: 0
I don't see any bad syntax in that reinvite offhand, but it's entirely possible that the UA in question doesn't like the 'topoh' droppings for some reason. Can you disable topoh and see what happens?
-- Alex