Parents have been calling me with lots of questions about when the right age is for a child to have their own cell phone. I don't want anyone to be kept on hold for this one, so let me provide some information.
The major reason a child would need to have a cell phone is for security, safety and convenience reasons, not because their friends have one, or to use as a status symbol. A child with a cell phone can signal when they are ready to be picked up from a sports practice, and allows you to reach your child if you are caught in traffic and cannot be there on time to pick them up from that practice. Many phones nowadays have GPS capability, so parents can at any given time know where their child is located, via their phone. On the other hand, most schools do not allow cell phone use during the school day, so there is no reason for them to really have one when at school.
Many parents tend to give phones to their children as they hit the pre-teen and early teen years when they tend to be away from their parents more doing other activities, otherwise younger children could certainly use a parent's cell phone or a house phone to make their calls.
If you do feel your child needs a phone for the reasons I have suggested, I would recommend a "time-limited" phone plan so that there are limited minutes for calls or text messages, and/or that there are parental controls on what numbers can be called out or come in such that your child can only place calls to you as parents or those responsible for their care, along with 911.
As to recent concerns that the low level of electromagnetic radiation cell phones transmit increases the risk for the development of brain cancers and leukemia, recent studies suggest that is not the case. However no one knows what the long term effects of decades of cell phone use will be, so it is still a good idea to make sure your children only use their phone when they need you, and not just to hear the sound of their own voices and that of their friends for hours on end.