In my limited experience, I had a problem with the registration to the VoIP provider (Unlimitel). IAX registration would come off and on. It turned out that my old SMC router did not do Quality of Service. Once I got a router with QoS (Linksys WRT54G) and assigned the highest priority to the port that connects to the asterisk server, problem went away. Just look for QoS in the router manual before buying.
George
