Triangulation is not an easy thing to accomplish at times. We have had climbers at Mt. Hood (Oregon), get into trouble at the peak of the mountain, be on their cell phones talking to family and have rescue crews unable to "triangulate" the hikers cell signal. In fact last year we had a group of three hikers all perish on Mt. Hood and all hikers had a cell phone.
The mountain shop offers special mountain location devices that rent for around 5 bucks a day. These have never failed a person in trouble on the mountain. But some hikers wanting to save a buck assumed that their cell phones would do the same thing as the mountain locators were wrong. dead wrong.