I have a CIX with two remote IPTs. The MIPU is on a public IP, no firewall involved. One of the the IPT's works fine, the other in a different city does not register.

I sent the user another IPT (preconfigured and tested here) to the remote user and it does same thing there. When I got the first phone back from her, I plugged it in here and it came right up.

She's on AT&T Uverse, and had AT&T verify all ports are open on their modem. Phone is plugged into the back of the modem.

Any suggestions?

AT&T DSL and UVerse modems have been giving me big problems with Toshiba IP phones. The only way I have been able to get the phones to register is to put the phone in the DMZ. This would only work for 1 phone. At another location we have a second router behind the AT&T router.