Good idea. Maybe have a way to synchronize all iphones in a crowd for changing color and frequency.

I wonder at what point a user will ask me to do something technically challenging like this.

They just did.

(Hint: potential users count.)

Synchronizing all the iphones in a room wouldn't be technically challenging assuming their clocks are all set at least approximately correctly, and you just make them flash colors/patterns that are generated deterministically using the system clock.

Actually this could look really cool!

There is no reason all phones would have the same time. I know some US phones sync the time with the carrier, which is a great function but not seen in the rest of the world.

You could use bluetooth, but then you have to switch it on.

You could use the camera to pick up the phones behind you somehow, but that would not always work.

Wonder if he can read input from the microphone and use that to pulse the light in time to music, or display a VU meter onscreen, or...

I remember jailbreaking my first iphone and installing a app, that did just that. The colors would fade in and out based on how loud you spoke. @andrewljohnson, If I were you I would make a short video of your app in action and post it up on youtube. I am sure that will get more people interested..

Haha, that's an interesting thought. I wonder if I will find some niche raver market on the iPhone from all of this.