Probably depends how hard the phone companies are looking at the data. If the cards are mostly idle then they probably don't impact the service at the tower and if there is no service impact then the operators probably don't care.

When you think about the sheer scale of monitoring every cell phone in the country it probably doesn't stand out nearly as much as you would expect.

I'm just salivating at the thought of being on the telco side with access to all the base stations and writing various visualizations/analysis to find hotspots like these, bet it's a lot of fun. :-)