What are the advantages using cell for teenagers?

I'm assuming you mean, "What are the advantages of teenagers using a cellular phone?" There are pros and cons, depending on your phone plan. If you're using a limited plan (IE: Not unlimited calls, texts and data) your bill can get pretty steep if your teenager tends to use it a lot, and not keep track of their usage.

Aside from that, having a cellphone for your teenager is usually a good idea, if you want to keep tabs on them (Though it's not guaranteed they'll answer the phone, or call you back). It's also a good idea if an emergency occurs, and they need to make a call.

If anything, I wouldn't suggest getting them anything too fancy or expensive, seeing as they're more prone to losing the phone, or having it stolen. A basic phone, unless you trust your kids, is usually a wise investment until they get a little older or more responsible.