Gizmondo has a nice write-up about a GPS-like add-on for the iPhone from Navizon. Using cell tower data, along with any local wifi that it can find, the software calculates your location to within a few hundred feet. While it’s not as accurate as real GPS, it provides a nice starting point for driving directions and will push your location to the Google Maps app so it will start at your current location.
The program is free for 15 days, then $24.99. More details on the Navizon blog.