Yes, GSM system needs to know the cell you are using during a call.
This seems to be known issue: How come phone exchange knows with whom I am talking?
It seems a bit silly to me, really. If cell is not known, connection can not be established.
On top of it: GSM is TDMA system, so it measures distance to the terminal in cca 550m steps.
It is called Timing Advance, it is needed in order to allign all incomming frames on cell receiver.
Now... Somebody looks at Abis (protocol between cell and Base Station Controller).
You can see measurement reports: with a cell, distance, measurement reports you can guess
approximate terminal location during a call. If you have enough neighbour cells.
They overlooked two minor details:
- you do not know whom you locate
- you have to monitor all possible cells
In fact, you have to double complete operator infrastructure: not an easy task.
On top of it: more and more GSM (BSS) is using IP as transport between cell and system,
especially if collocated with HSPA+ or LTE. IPsec is used on this interfaces.
Even operators, who need this data during system tuning and debugging, have problems to get it.
Special test SIM cards, protocol probes after SGW etc are used. Normally, such tests are prepred
and executed on selected cells: getting all data history for all users is beyond reach of most operators.
It is much easier to get my location using different methods, like asking me politely ;-)