I think it would be best to get her a pay as you go type of phone/plan. If you are footing the bill, you can give her X amount of money for minutes per month, and then when she runs out... oops, she has to wait until you give her the next bundle of money/minutes. When your minutes run out on a pre-paid phone like that, their phone becomes a brick until more money is added to the account. Great idea for getting her to manage her time and to become more responsible.
Of course, going this route is pretty much guarenteeing you a lot of "Daddy! I need more minutes!" nagging over and over
Just don't get the girl a smart phone. That can be a present to her when she is making enough money to be dropping $60+ per month on a plan.
