A good introductory article on how GPS based smart phones are creating the plattform upon which augmented reality applications can be developed. Heres the excerpt and link:

The world as we know it is about to change once again for personal navigation devices.

"Mobile Augmented Reality overlays your location with a multitude of real-world data. Your smartphone camera sees the real world that you see. Overlays identify what you are looking at or pointing to and provides a host of possible information such as identifying restaurants, shops, historical landmarks, public transportation gateways, and various points of interest. All this delivered to your screen. You control the amount of content and can specify different views, if you want to see what's around you from different perspectives, from standing on the street up or standing on a roof of a building. Each identified object will provide the user with additional levels of information such as a picture, address, and phone number of a restaurant, its menu, its interior, user comments, and their website. For travelers these new devices are really useful, as you can walk through a historic district of a city, point towards a building, and see its history as you're looking at it....... READ MORE