You have to unlock your phone to work on all networks I believe (each provider run on there own frequeny). I did this with my old phone that I bought off ebay, it was something else and I needed it to work with cingular. You can usually find kits on ebay ( just a wire to hook to your computer and a code) and unlock so it works on all providers. But this will change from phone to phone, some are more advanced I think.

2002 WRX
Eclipse RS-T..sold