Please find out the problem with the following steps
1. Your ATA (Analog Telephone Adapter) can be installed behind your home router;
2. Please try to connect your ATA directly to your Modem. If the issue is resolved, you need to focus on your router;
3. Some routers in market are SIP aware device that could cause problem. Could you login the Web GUI of your ATA? If yes, save the Web page and send it to me. I could find out which parameter is incorrect;
4. If you could not login the Web GUI, please use ethereal or wireshark with a Hub (not switch) to capture all packets in/out your ATA. The problem you have could be caused by signaling or media issue. If you could get the UDP trace, please send it to me, and I will be able to find out the cause;
5. Please do not enable SIP ALG on your router if your router has that parameter. Enabling SIP ALG could cause SIP SDP parse error;
6. You cannot use port forwarding on your router to resolve this issue since media streams (RTP streams) use dynamic port;
If your ATA comes from a service provider, you could call them to ask if your router is support.
Let me know if you need further info.
Support from Bell Canada