For some reasons some phone only work with some cars. I looked at an Acura a while back and they has a list of phones that would work with it. It was a short list too. What I would do is take the car with you when you go to buy the phone and have the salesman come out to your car and see if it works.
You might want to read this
http://www.cellularphoneforums.com/t168036.html but it confused me more than it helped.