Our eldest is 9 and she got a cell phone from her birth mother for her communion.

DH and I felt that 9 was too early for her to have a smart phone and thought about taking it away. We sat Nicole down and told her what responsibilities she would have: a) if she loses the phone, it is gone; b) she will have to earn the money that goes onto her pre-paid card; c) phone is to be OFF during school hours unless an absolute emergency.
Her phone is programmed so that she may only call me, DH, my mom, my grandmother and a close friend of ours. She also may not use the internet. She only uses the phone to ask if she can stay at a friend's house longer, etc..