The Parrot solutions are also very interesting.

But the benefit of the Oxygen unit is the you can play apps etc.
So you can use your navigation app on the iPhone showing directions while listening radio, or mp3...

Take a look at this video (sorry, don't know how to integrate it directly)
Dailymotion - OXYGEN AUDIO lance O Car ( Vidéo O?Car Officielle) - une vidéo Tech & Science

Regards
Markus