Navizon Using Tower Triangulation
If you've hacked your iPhone, you may be aware of a positioning app called Navizon which maps your location via tower triangulation and the presence of known wi-fi hotspots. That version costs $25, but there's a new version of Navizon now available. It's called Navizon Lite, and it provides location awareness based only on tower triangulation. In short, it can tell where you are (roughly) based on what kind of signal your phone gets, and skips the database of wi-fi hotspots. It's tough to beat free, but you do have to hack your iPhone to get it to work in the first place.