Although many schools ban them, a frequent debate among parents is "Should teenagers have their own cell phones?" and if so, the debate continues to "What age is best?"
No one knows your teen better than you do. Children mature at different rates and the 13-year old in one home may be ready to handle the responsibility of owning a cell phone while the 16-year old in the next house is nowhere near ready. The first thing you need to do is make the judgment call on whether or not your teen is ready.
Next, what will the phone be used for? Talking with friends, text messaging, instant messaging or (d) all of the above. If you add your teen to your own cell phone plan, make sure you read the fine print and find out if there is a limit to data (ie: text messages, instant messages and downloads) or you could get a very shocking cell phone bill the following month.
One solution many parents use is to get their child a "Pay as you Go" type of cell phone plan and then let the child earn their cell phone minutes through chores and other activities such as mowing the lawn, getting straight A's, babysitting, and more. The phones available on the pay as you go plans generally are bare bones and many don't have cameras, instant messaging capabilities or other "extras". You can usually get around that by purchasing an unlocked cell phone and switching the SIM card (little card inside the cell phone usually under the battery) with a better quality phone and using all the features on the pay as you go account.
If your child is showing a level of responsibility that shows he or she is ready to keep up with a cell phone and use it responsibly, give your child a chance to show you how mature they are and let them have a cell phone of their own.