It uses WiFi. My ISPs SIP server is sip.xs4all.nl, port 5060. Same for proxy. My ISP isn't blocking any ports for I can define which ports my ISP should block, and its only blocking incoming SMB/CIFS. Not SIP. And certainly nothing outgoing. In fact, they want me to use SIP, and I do with a POTS phone connected on my DSL modem. But I'd like to use my NIT as well. Again, with Gizmo and Fring it works, with the normal SIP client it doesn't.