This is sooo cool. People at sprxmobile.com made a special augmented reality browser, called Layar. What is does is that is show you digital reality over the physical reality in the screen of your phone. For example you point you phone at a house and over the camera picture it is shown if it is for sale and what is the price. Look below.
All kinds of interesting applications can be made with this. In a project in the Amsterdam Living Lab we are piloting an application like this to find out how people will use such a service, especially when they are able to leave digital information behind that others can see with their phone. It may be that we will use the Layar technology instead of the home grown one. Of course a phone with and a GPS and a compass is needed like the Google phone or the latest iPhone 3gs.