Collecting data from GSM devices
You can use GPS to calculate the position of your own device if you happen to have a good enough sky view to receive the GPS signal.  Otherwise, GPS is not useful.  GPS is the Global Positioning System.  A GPS receiver uses signals transmitted by GPS satellites to determine it's location.  However, the GPS signals are very weak and cannot penetrate effectively through buildings so GPS is of little use indoors.  Also, a GPS receiver can only determine the location of it's antenna.  It cannot be used to determine the location of another device.  

As for tracking GSM devices, the best you will be able to do is radio direction finding, and then only when the units are transmitting.  It may be possible to extract some information about the GSM devices, but it will require a highly specialized receiver.  A software defined radio unit would probably be the most economical route.  Also, you would likely have to break GSM's encryption if you want to gather any information about these devices.  This is likely illegal.  Another possibility is to build your own base station and set it up so that the phones connect to you.  However, this is far more complicated and even more illegal because you would have to transmit on licensed frequencies.