Go to a pc on their network and go to the Command prompt, enter C:>ipconfig

If it comes up like - pick a higher number for the phone system like .25 - copy gateway, subnet into 7100 programming. The 7100 sits on an internal address.

Then go back to the PC and make sure you can ping .25.

Now, either you or their data person can set port forwarding from the wan address to the 7100's internal address you have assigned. You can ID the wan address by surfing to www.whatismyip.com

Port forward:

Used for Ports

IT Programming tool 5003, 5090 TCP/UDP
Voicemail programming 443 TCP
Voicemail activity 23 TCP /telnet