This. I laugh when someone comments that they don't like the idea of RFIDs, or cameras in public places, or other ways the "man" might track them, then they pull out a cell phone. Cell phone companies have been able to track phones from DAY ONE. If you are within range of three cell towers, they can pinpoint you. Two, and they have a general idea. One, and you're within a circle around that tower. They don't need GPS, they can use their basic infrastructure.
When cellphones started to become easily portable and theft of cell codes and the phones themselves started to rise, I remember one company (forget which) announcing that they could protect their customers by monitoring their usual useage areas and tagging calls from outside those areas as potential theft. That ability hasn't gone away.
Come to think of it.. credit card companies do that too....
Where you are and what you are doing is already being tracked, compiled, and sold to advertising companies. Grocery card? Good for the sales, but don't think for a moment that Kroger/Giant Eagle/etc. aren't compiling what you buy into a database so they know what to stock in each area.
There's no way to stop it. Data flows both ways.