Police, GSM producers and army can do that. Also you can just find the place where the last call has been done or received from. You cannot use it like a GPS.
It is simple to do but you need acces to the GSM received placed in towns and/or satelites. For example you wanna know where did your gf called last time. You search the last call in her GSM operator database, find the last receiver trough which the radio wave passed first time in it's way to the GSM operator server and then the direction where the wave came from and it's frequency. With the frequency you can find the distance between the mobile phone and the GSM receiver, that and the direction should point the place where the phone called last time. Simple thing, just need access to FBI :D