I have T-Mobile with Sony-Ericsson T610 and have had no problems linking, calling, etc. with the car.

My new toy, however, will be the new HP IPAQ h6315 which I expect to receive sometime this week -- I am really excited, as I have been carrying around a Dell PocketPC and my phone banging together in the same pocket for a year already.

It's funny that the car I bought is mandating the other electronics around it.