First of all if you are a minor then you can not sign up for cell phone cell within any provider. You must be at least 18 years old with a drivers license and have credit history. However, you can sign up for prepaid cell phone services which do not require any contract any or credit check. No age limit is require on prepaid.
If you have a friend or your parents and they are over 18 then they will be the primary person on the cell phone account when he or she sign up for cell phone service. They can add you as the secondary line if they wish. Other than that you can not be the person who is the sole owner of the account because you are a minor.