Phone companies can work out the locations of each cellphone to near GPS accuracy - it's trivial to do.

Wanna bet that data's not finding its way into the NSA database as well.  Phones ping the cell tower every minute.  Say a 100 byte GPS location code per minute, for each cellphone in the US (and 70% of us have 'em) = around 28 TB per day, which seems in the ballpark to make the database large enough.