This happens because some routers (Belkin is a real problem when it comes to all VoIP equipment) do not support the SIP protocol properly and thus do not pass SIP signals properly through the router to the your hosted pbx provider and thus x-lite cannot connect or you experience other odd issues (like the phone not ringing when it should). There are quite a few routers that I personally know do this like 2wire, belkin and netopia, they are all terrible routers when it comes to voip. Whats the solution? Get a router that's voip compadible. I personally like Linksys routers and haven't had issues with any of them. Sometimes you will also end up with a situation where you have a router plugged into what you think is just a simple modem. But often in the past few years modems have built in routers so you have two DHCP servers and the router is actually connected to another router/modem and you end up with double NAT issues. The solution to that is to make sure your modem is acting just as a bridge and not a router (you ISP can tell you have to bridge it).