Actually, I did buy one two years ago. A nice CAN-BUS Auxiliary Input Adapter. But the directions said I had to dismantle the entire dash of my Fusion to get at it.
It looked like too much work so I put it on my electronics shelf. I just went over to the shelf, and it is still there, collecting dust on the plastic zip lock gallon bag I put it all in.
I probably need to put it on my growing todo list.
Hmmm...
The ones I was referring to just plug into the cigarette lighter, and a mini audio jack goes to your phone or MP3 player. No real installation.
You tune your radio to a dead FM frequency and match it with the transmitter.
Bang! Your signals goes into the radio via FM signal.