Contracts entered into by a minor are voidable by the minor before they reach the age of majority or within a reasonable time thereafter.  Bascially this means that the minor can break the contract anytime before they reach the age of 18 or a short time after they reach the age of 18.  However once they reach the age of 18 and they validate the contract by making a payment or performing to the contract they can no longer break it.  The only exception to this rule is that the minor is liable for the reasonable value of necessities such as food and shelter.  Cell phones, cars, and most other things are not considered necessities.