Can I have my iPhone navigate through my car's stereo? Is there an iPhone navigation/GPS app that will announce the turn-by-turn directions through a car's stereo via bluetooth?

I already have my iPhone synced with my car via bluetooth for calls, so I'm wondering if any of the navigation apps can also take advantage of the connection?

I'd rather not have to buy a separate iPhone car kit or a FM transmitter.
Can your car accept the iPhone's music audio as an input to the stereo? On my care (Acura TL), the bluetooth profile lets me play iPod music through the stereo when the phone is paired. As a result of that, ALL of the phone's audio plays back through the stereo... including text alerts and any apps that play back voice sounds (navigation, etc).

It's probably too simple an answer, but it's worth checking to see if you can pair up using the audio profile for music -- in which case you'd get the phone's other audio as well.