I've heard that Firefly is best, but I do not believe that kids should have cell phones. If you are a parent, I'm sure that you could understand this reason.
Cell phones are just another health liability that is possible of causing serious damage later on in life.
In the air, there is something called Electro-Magnetic Chaos (EMC); this is an invisible electric field that causes transmitions to be made to another phone. (Towers just aide in directing the signal, so it doesn't get lost or create an interferance.)
Also, with cell phones, this chaos is directed into one place when you're talking, or just carrying it around (on or off): the brain, and the body. This type of damage is very extensive and can result in major health problems later on in life as they continue to use the phone.
If you would like more information, I suggest extensive research.
I hope this helped you.