Cell phones are not a guaranteed item that will help you, or all the reasons mentioned, but my reading of SAR events, now as compared to the pre-SAR era, is that cells often initiate and facilitate rescue operations.

A call comes in from the victim(s) in the field, giving their location, or at least landmarks, and the situation. This is way better than the call we used to receive from someone who could only tell us that Joe was overdue and he went out hiking somewhere....

Most cells have GPS capability, and, if not, their approximate position can be roughly determined from the cell towers involved (so I am told - I know zilch about the technology involved).