It is unlocked GSM so it can be used with numerous carriers. Not the greatest phone in the world though. Lots of cool features but extremely uncomfortable, very cheap feeling and the reception could definately be much better. Speakerphone is probably the best on the market though. Extremely loud ringers and awsome camera. Quick shutter speed almost no blur with any movement.
It can be used on Cingular and Tmobile it is gsm. It is setup to run on Tmobile though..... it will work on Cingular but you need to program the text messaging settings in it to get the text and pix part working.