I just purchased a Sony XDP-MU110 Digital Link Sound System from crutchfield, it links your iphone (4s and lower, my only complaint) to the factory head unit (also bumps the sound quality a little bit). the original price was 500, but it's marked down to 49.99 (free shipping) just figured I'd put the word out for people looking for a way to use your iphone as your music source.

http://www.crutchfield.com/S-cKqAA0Z...nd-System.html