Mark Cuban just sent an enthusiastic tweet about Paranoid Games' location based iPhone title Insurrection, that's releasing on the App Store July 4th (check out the backstory video). I have to agree this looks pretty interesting, particularly in light of rapid smartphone consumer adoption of services like Foursquare and Gowalla... which are inherently much less fun.
However, this is hardly an original idea. 10 years ago a Swedish company called It's Alive! created and deployed a location based game called BotFighters in several European countries, that used WAP & SMS. As has been typical in this space, the It's Alive! guys were way, way ahead of their time and their company, which eventually (ironically?) merged into another called Daydream, was soon gone but not entirely forgotten.
I think Paranoid Games has the timing right, so now it comes down to execution and marketing. I wish them luck.