We did this in Iraq. When we built their cell phone infrastructure and cell towers, we ultimately used it against the insurgents. We even remotely used the cell phone network to track certain individuals and use them to turn microphones on remotely to evesdrop. The amount of data we must have collected would be astonishing.
We could tell what "phones" associated together, what users were even in the same car together , daily habits and tendencies, their locations, phone records, microphone activation to evesdrop on conversations etc...
There is some scary technology most people are oblivious to our governments capabilities.
No joke..more and more I'm thinking of trading in my "smart" phone for a dumb phone