Today Google revealed the second version of their Google Maps application that can now localize your position based on the cell tower information triangulation. The new "My Location" feature allows the convenient use of Google Maps on handsets with or without GPS.
The mobile tower information allows the "My Location" feature to pinpoint your location with a relative accuracy of around 1000 m. That's not that great, however reportedly, in certain cases accuracy can go to as high as 200 m. Here is the official Google video explaining the basics of the new feature.
The service will work wherever Google Maps for Mobile is currently available. The Google Maps for Mobile 2.0 application can currently be installed on Java, BlackBerry, and Symbian S60 devices. There is even a native version of the application for Windows Mobile. Google Maps for Mobile 2.0 is still in beta development but it works reliably and can be downloaded here. Java phone users should point their mobile phone browser to http://www.google.com/gmm in order to download the Java application.