T-Mobile and a Nokia 3650 work just fine for me. The 3650 or 3660 is a GSM phone, which means AT&T Wireless, Cingular or T-Mobile (latter two use the same network through roaming partnerships) are your choice of carriers. I'm sure there are other BT phones now though.
I have Cingullar and a T616 mobile. I have no problems with either and get great reception in my Prius. Great phone.
Cingular and Ericsson T616. Audio good listening to a landline phone. Very garbled when listening to another cel phone. display unreadable in sunlight, even in the car. Tollhouse
Great deal on cingular I have a Motorola v600 which I'm very happy with except the transfer of numbers to the car is a bit of a pain as I think you have to do it one by one. The other problem I have is that I have to turn on the bluetooth on my phone each time I get into the car. I don't know if this is a common problem with all phones though. It would be nice if the bluetooth(on the phone) was always on. The reception is awesome though. I got the phone through a guy in L.A. that works for cingular and can get the things for great prices. When I got my phone it was going for about $300 and I got it for $80. If you're interested, check out the cingulair website to find a phone Cingular you like and e-mail him at [email protected] Don't know if he'll remember me, but tell him Chris told you about him. I think the actual deal is 75% off the phone and like 10% or 20% off the monthly rates. He's a good guy too.