What model car? I've only used a Garmin GPS (didn't work too well, too much ambient noise) and a bluetooth headset/earpiece to pair with my Bold 9650. It may not be an option for you, but it's simpler for me to just not answer the phone while I'm driving - let it go to voicemail and grab it when I can. Too many people can't hear me clearly and I find it distracting to try and focus on a phone conversation while driving... it can wait.
Just my 2¢