How old is appropirate for kids to have their own cell phone?

Lost Art of Talking: Unless a child needs a cell phone for safety, i recommend waiting as long as you can. Nevermind radiation, cell phones can pose a hazard to personal safety; academic achievement; and, importantly, normal, healthy interactions with friends and family. Cell-phones also tend to distract from higher priorities, and, with web access, they open the door to potential moral decay.

Large variation: The answer to this depends on your family values and your family dynamics. Probably, there is no need at all for a child or teen to have a "smartphone" until they have a job where they can pay for the phone. On the other hand, it may be completely reasonable for a school aged child to have a cell phone to communicate with parents and family. Beyond that, there is no absolute answer.