I would like to know as well, if it is even possible. My deck has a usb slot and it works, but only plays music through media player, which is fine, but really like Pandora as well.
If your head unit has some sort of Auxiliary slot, you can just plug a 3.5mm (headphone jack size) cord from the head phone slot in the phone to the Aux slot in the unit. Or at least that's what I do to play all my music from my phone (even Pandora)... There are probably other ways though, also.