I belive that cell phones are "mostly" line-of-sight. If you are in a canyon, there is a posibility that the signal might hit some trees and bounce around enough to reach a tower. Of course, the signal loss is tremendous, but any signal is better than no signal.

Note that the Kim family had a ping recorded on a distant cell-phone tower. It is possible that a cell phone amplifier might have allowed them enough signal to send a text message.

Of course, if you are going to spend $400, you might as well get a PLB <img src="/images/graemlins/wink.gif" alt="" />