If you have a mobile phone, you can be tracked, even if there is no GPS on the device. Besides this if the NSA chooses, they can track practically ANYONE in the world, all they need is a mobile number. I would not be surprised if this is actually one of the tools they have.
How?
Due to the nature of how GSM and mobile operators integrate when roaming. When a mobile operator signs an international roaming agreement, they setup signalling links between their switches and VLR's (Visitor Location Register).
The mobile operator in the visited country needs to authenticate you against your home network, this happens via SS7.
Once this link is established, it is assumed to be trusted, and most operators DO NOT apply any filtering on these commands. So with a carefully crafted SS7 command, you could request the location of a mobile subscriber, even if they have not even attempted to join your network.
Now here is where it gets interesting, get access to send ss7 commands from an operator with many international roaming agreements, and you can get details on practically any subscriber. Get access to 2-4 (i.e AT&T, T-Mobile, Vodaphone) of these massive tier1 operators, and you can get the location of practically everyone with a mobile handset.