My 12 yr old doesn't have a cell phone. She really has no real use for one. She rides the bus to and from school. The two times she missed her bus, she called me from the school office phone. I take her to her activities- fencing and an art class. I pick her up once they are over. On the weekends, she might go to her friends' houses but really has no need for a phone. Does she want one? Of course. But she doesn't need one right now.

http://www.youtube.com/watch?v=5HbYScltf1c

Here, let Louis CK help you out with the "why not?" part.