Yep, a competitor's pp phone is a good idea but so is carrying/buying a phone card or carrying coins for regular old pay phones. During an emergency, the cell system is more likely to be overloaded rather than just being out of range. When I vacationed in Yellowstone last year I was out of cell-phone range for the majority of the trip. "Ahhh, peace and quiet! I loved it."

Or of course you could learn semaphore and smoke signals!