Tritch is totally correct. With your initial configuration, the ONLY way it would work properly is if you were paying for 2 IP addresses from your ISP, or the Modem was ALSO a router, and was putting out 2 Private IP addresses. e.g 192.168.0.10 and 192.168.0.20. If the input (WAN) of the router and the input (WAN-Internet) connection of the voip adapter were getting the SAME IP address; because the modem was only putting out 1 IP address; then all hell will happen.