I have been searching all over the internet on how to play Pandora through my radio...finally found a way that works!
1. Put you radio on AM/FM.
2. Plug in your IPhone and turn Pandora on.
3. Hit Play and start playing a song on it.
4. Click media on your head unit, when this happens the music stops on the Pandora.
5. Hit Play again and Boom it's playing through the radio.
I have a 2010 Audi A4 and this method works each time.