Seriously 75% of kids 12-17 own these phones now so they seem to be as common as shoes. My neighbor's daughter has one. She is 8 but at her rather toney elementary school there was a big hooptido about wearing them on the geek belts to class and what to do with them during tests. The kid is never out of mom's sight - trust me on that and I'm not sure of the danger she is except to die of peer pressure.
I think there needs to be a common sense rule. If a kid, say up through high school, meaning when age wise they have zero common sense anyway (kidding!) they get phones that don't text, don't have apps, they just make calls and only home or to the parents work and cell phones. They have GPS locators so you can find them in an emergency or moment of angst. They have a call number limit...say 3 anyone calls a day...period.
Or you can put a couple of tin cans connected by string in their backpacks and let them make do.