I answered you on the other post you made that I think may be the same problem: Netvanta 7100 remote phone message button does not work
make sure the sip alg is off on the 3120 with the following command from global config mode: no ip firewall alg sip. If that does not work we will likely need to see the configurations from each unit and debugs from the 7100.
Please let me know the result. If that does not fix the issue we can continue troubleshooting, but I will need to see both configurations as well as the output from a debug sip stack messages and debug voice verbose from the NetVanta 7100. You can submit them with the instructions below:
Open Internet Explorer web browser on their PC
Type the following URL: ftp://ftp.adtran.com
Press the Alt key, click View, and then click Open FTP Site in Windows Explorer
Double-click the "Incoming" folder
Drag and drop files from PC into the Internet Explorer window
Reply to this post with the exact filenames used so we can retrieve the files
Please try turning off the NetVanta 3120 SIP ALG first though.