I downloaded Layar in my iPhone, and the idea is great.
You can see the world with your iPhone (like when you take a photo), and different things could appear in your mobile screen.
You can play, you can see more information in a museum, etc, depending on which layer you use at the moment, or you can virtually walking on the Layar office.
Have a try to download this application in your iPhone or Android. (Layar)