One think to consider in a "Wilderness Survival Situation" where your cell phone will normally be off because you are out of cell phone range is that a cell phone is a Line-of-Sight communication device. That means that you can climb to high ground (Insert: a mountain or large hill)and you may be able to call out on the phone from a location far from any cell tower. I have actually experimented with this in the Rocky Mountains and reached a cell tower over 50km away.