Your youngster will probably start to hound you about a cell phone somewhere around the age of 11 or 12. When you can't take the badgering anymore, toss them a phone from a discount store. You have to prepay for minutes and texts (which you will soon tire of), but it will help you determine two things: Is your tween is responsible enough to keep track of a phone for at least 3 months and what sort of a minute/texting plan you are going to need when you add Junior to your plan.
Scoff if you will, but right about the time your child enters junior high, your every request for assistance will be met with huffing, puffing, eye-rolling and attitude. It's fascinating to note how much more agreeable your pre-teen can be when you dangle an unlimited texting package in front of her. And once she has it, you'll notice how helpful she becomes when you threaten to take her phone away from her. Parenting is all about adaptation.
Kids in junior high become increasingly involved in social activities, but until they're old enough to drive, they have no way to get around. If your a family with a busy schedule, you won't be able to get your child everywhere they need to be, so all of sudden your pre-teen will be bumming rides with other parents and friends. A cell phone will help you stay on top of where they are, what they're doing and who they're with -- as they'll have the means to text or call you with information like what time they're leaving. And if they don't like that, then please refer to "bribery." If you are paying for the phone and the plan, then it is yours. Thus, the phone can be confiscated by you at any time.
When you have more than one teenager (and more than one teenage driver), a family cell phone plan can really help out. Chances are, the whole family will be going in different directions at different times and a family plan can help keep everyone connected. As your children grow older and have proven they can handle the responsibility of a cell phone, you may even want to consider getting smartphones for the family. There are countless applications available to make family life easier, the most obvious being the ability to sync everyone's calendars. Don't be afraid to have your teen pay for their portion of your family plan. Data packages can get expensive, and the teenage years are a great time to start teaching your child financial responsibility.