Comment by rjmunro

I believe they switched to pagers because their location can't be tracked. Every pager message is broadcast across the whole country and the pagers just listen to all of them and only tell the owner about the ones meant for them.

A phone has to at least tell the nearest tower that it's within range so that the tower can know to send it messages. After that, when it get's a message it sends some sort of acknowledgement. In theory anyone can pick up those messages with a phased array or set of directional antennas and get a directional fix on the phone.