http://www.neocaraudio.com/
These guys sell iPhone car stereo integration kits that integrate your iphone fully into your car stereo system. I might add that I am a complete idiot when it comes to doing any sort of work on cars or houses..but, this was very easy and straightforward to do.
I now can plug my iphone in and have all my music, audible navigation, internet radio..and take hands free calls all over my car audio system.
As a last point, I had a couple tech support questions..and I was able to get a knowledgeable human being on the phone within 3 minutes of my call. I almost passed out from the shock.