A pair of security researchers has discovered a number of new attack vectors that give them the ability to not only locate any GSM mobile handset anywhere in the world, but also find the name of the subscriber associated with virtually any cellular phone number, raising serious privacy and security concerns for customers of all of the major mobile providers.

via Researchers Hijack Cell Phone Data, GSM Locations | threatpost.

They use the caller ID database which is pretty much open to everyone, because all the providers need to get at it.