I've been in a few situations where I'd think something like this would be usefully, I've also have an imagination so maybe this is impossible.

My idea and I'm sure others have thought of this is an app that would allow multiple phones (Pre's, iphone...etc) to ad hoc link up over bluetooth or wifi to syncronize music play back.

For instance, one person's phone would be the host (DJ), the other phones would basically just be speakers being fed the music from the host phone. Ideally, not everyone would need to posses the song file on their phone.

If it was done, and the ad hoc was strong enough, it would make a really neat commercial to show the power go out at a house party or something and have everyone flip on their phones and play synced music that way, letting one phone be the DJ. More or less it would probably just a parlor trick among friends though.

Maybe the app could have a disco lights feature (ideally the DJ phone could choose the disco lights theme), or at the very least display the song's name on everyone's screen.

Multipe types of phones would be nice for a global perspective, but I'm first thinking of the Pre.

Let me know if anyone decides to take a crack at this...or at least a nibble.