Oh, I see. That wasn't exactly a secret prior to this, though - I thought you meant some novel way of finding crossers by tracking the phone, as opposed to exploiting existing information available on paper maps or suchlike.
I hadn't thought of that, but if people actually make phone calls, their location can be approximated based on the cell towers that picked up the call (or so I understand -- I imagine there are folks here who know way more about that process than I do).
