well if i cant get it to work with my cars handsfree than ill most likely get this for my car. My friend was a beta tester for the product so i know its good. He streams music while on GPS, and it works fine, doesn't stop the music for the GPS to speak, just lowers it a little bit allowing your to GPS announcements a tad louder then the music.
http://www.myventuri.com/overview.aspx