So they got too near a gas pump, or what. How do cell phones work without towers, and why bother banning the phones when you can just turn off the service?
Please read my reply #32. I think it would answer your question.
I am sure a cell phone can be used to trigger an explosive without a tower. It emits radio waves. You just have to have a receiver of the right frequency. But they why use the cell phones? Maybe it's cheaper.