IPhone app to follow/navigate an imported .gpx

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.

You can use this application.
It uses an hidden file stored on the iPhone recording an history of location. It has been a little buzz since yesterday when it came out on almost all media worldwide.
From the description of how to tool is working, it will even work with a backup file of the device. So you can use it on a Mac where the iPhone has been sync'ed and backed-up.

PS:
I don't want to go in the discusion "is it a good thing to track people etc...". Just trying to answer the OP question...

edit
Now available for windows on this link.