My main router is a rt-n66u with tomato, I didn't have to do anything on the main router (all I did was add the mac address and IP address of the WRP-400 to the QoS classifications, but that is so the voice doesn't cut when people are downloading or whatever). Here's my setup on the WRP-400:
Thanks again. I got it to make and receive calls. However, after getting connected, the line is just silent. Nothing goes through... I might as well put the WRP-400 in front of main router for the time being (with the main router and DMZ and all unneeded features on WRP-400 disabled). Time will tell if there are any downsides to that setup.