Are you going to write the actual augmented reality engine, or are you looking for an engine to use that you can build upon? My engine tries as much as possible to hide the actuall implementation of location and orientation handling so that the package user can concentrate on other things. But if you are interested in the actuall implementation, I would be very happy to provide details about how I have done.
If you are looking for an engine upon which you can build further, my package does provide some support for that, even if its not in any way complete. Download the application from lesson 4 to see if that is anything like what you are looking for. It can take up to a couple of minutes before the phone recieves GPS signals, but ones it does all boxes should disappear from the screen. When they do, press the "F"-button to fix the origin at your current possition. You should then be able to walk around between the blocks and look at them from different positions. (Might have to refix the origin a couple of times if the GPS not provides an accurate position the first time. If the boxes jumps alot, then keep refixing until they "calms down").
All of the lessons after lesson 4 uses the GPS position. But I have noticed that the more complexity that is added to the scene, the more likely is the GPS to stop giving signals to the applications. It seems to be that the GPS is among the first things to be cut of as you run short on resources. So, I therefore advice you to start trying with the fourth lesson, and then try out the other if they prove to work on your phone.
If you want something that is more complete and reliable, I don however advice you to look at one of the Augmented browsers instead. My package is however more towards a "local" augmented reality, and might actually fit better if that is what you are looking for.