If they are connected by a VPN then there should be no ports being blocked. Are you sure its a VPN setup or are they using port forwards? If its just port forwards then a required port range is missing.

When you said the IP phone will work, have you tried one at each site talking to the remote system?


Cheers, Dave.
Eco Communications
Selling and installing Ericsson BP150/50/250 from 1996 to 2005
Samsung selling and installing since 2000
Toshiba selling and installing since 2004
Microsoft NT and SQL certified (10 years ago...)