you can use instead of an SIP if a normal GWx interface. Here you have the possibility to use a GW without registration and also SIP. Did you have a IP302 with the small memory? Or did you have the "big" one. Then it is possible to use another Firmware.

http://wiki.innovaphone.com/index.php?title=Howto:Firmware_Upgrade_V11r1_V11r2#Memory_Considerations

http://download.innovaphone.com/

http://wiki.innovaphone.com/index.php?title=Reference13r1:Gateway/GK/GW

Gerrit