Why this technique is generally useless (Score 1)

Well, given this capability, the first thing I'd do is to take out every cell site.. very easily mapped in advance by satellite and by reviewing publicly available engineering documents. No cell sites - no receivers (and many unhappy yuppies, a collateral benefit). It could be useful if you suspect in advance a single-aircraft covert ops penetration mission, but it's likely reconfiguring the cell sites would be detectable by the drop in performance of the PSTN and thereby tell the other side you know they are there... itself useful information. Watch for this in a Tom Clancy novel coming soon!