I am pretty sure that most newer cars integrate bluetooth so that you can use your phone and your minutes in your car without the need for another account. I have a newish GM car that works this way with my old iPhone (I love it). There is a mic in the pilar near my head and the sound comes out the speakers. I think Mazda offers this feature and would be surprised if it wasn't standard on most brands. You can opt to have satellite phone coverage using OnStar (GM), but you don't need to if you are only planning on using your phone with your current carrier. So look for "bluetooth integration" and you should be good to go.
I am in the market for a new car. Our area will implement a handsfree law soon, so I won't be able to drive and talk on my iphone. Does anyone have any comparisons on handsfree technology? I understand Ford has an exclusive arrangement with microsoft. I believe i could make and receive phone calls with this technology but won't be able to receive text messages. Does any car manufacturer have an arrangement with Apple? My office is my car, so this feature is quite important to my purchase.