I have used wireless transmitters with my ipods and iphone in my car and they have never worked well. I keep going back to my old faithful which is a cassette tape with the wire attached that I plug into the headphone jack of the iphone. To my surprise a few months after I bought my headphone I discovered a neat little feature.
One time the phone rang and I answered it but didn’t take the cassette plug-in wire out. All of a sudden I heard the person’s voice over the speakers in my car. I lowered the phone from my ear and talked to her as if she were in the car with me. It was a pleasant surprise.
As a result of this discovery I decided not to buy a bluetooth for the phone. I had a ‘jimmy-rigged’ hands free blue-tooth already in place.
I haven’t checked to see if others know about this but it is my favorite ‘trick’ for my iphone.