On monday I recieved a Siemens Gigaset C685 IP from the UK to replace my Linksys SPA942. I plugged it in and set everything up and it was working fine, but a few hours later my ADSL modem started soft rebooting every few minutes. I'm looking for advise on what might be causing this.

The base station for the IP phone is plugged into a Belkin F5D7230 wireless router (by ethernet), which is in turn plugged into a Telecom NZ supplied Thompson ST5x6v6 ADSL2+ modem/router.

Unlike the other wired devices plugged into the Belkin, the link/activity light shows up amber for the port the IP phone is plugged into, and green for the others. Likewise, if I move the IP phone to a different port of the router, that port lights amber. Not sure what this mean.

The modem seems to be doing a soft reboot, but I cannot see what causes it as the modem only shows me starts from the last reboot. Does anyone have any idea what could be causing the IP phone to make the modem reboot?