You can use the monitor commands or the EASY SCAN commands. AT#MONI gives you the values listed das below:
#MONI: TDC MOBIL BSIC:54 RxQual:0 LAC:0155 Id:1282 ARFCN:46 PWR:-77dbm TA:3
TA:3 means Timing Advance of 3.
If you buy the Cell IDs database from your local operator, then you will now which Cell IDs are in a city. You can also do it by probability calculation. In cities you will always find more base stations then outside of the city.
A GSM module with micro controller on same PCB can do that job. You collect the Cell IDs and forward it by SMS or GPRS.
Are you asking for a database which shows which mobile phone is registered to which base station? The GSM operators in some countries offers ready to use access to such GSM based location services.
If you would not like to invest in an own location based service, then most time there is a specific service necessary. In Germany, UK, France and a lot of more countries you can get location services based on a special location service contract.