And Wifi base stations too, though not to the same level of accuracy as GPS.
Google's Android phones and Sony's PSP PSVita have similar location services through wifi triangulation when GPS is not available. You will need a data connection for it to work.
Originally Posted by
gnaget
The Navi in my car even works below ground in the Yamate tunnel, for example.
Factory-installed automotive navigation systems may receive speed and steering input to continue estimate your location when GPS signals are not available. This feature is called dead reckoning. You can also achieve the same result with accelerometers.