[Nosey]

just my 2 cents worth, but I actually think it's a bad idea to lock her out of the phone at a certain time, and here's my reasons:

she is out after 10pm with family (or friends) and something happens, emergency, etc, yet you have the phone auto-lock her out at 10, now she has no way to dial 911, or she is at home, and a fire breaks out in the house, she can't get to a land line and you have locked her out of he phone, and about a million other reasons..

if she was my child, I would feel pretty bad if she had a cell on her but unable to use it for an emergency and something happened (if she didn't have a cell and something happened, I would feel bad that I never got her a cell lol)

I think the idea of good grades, etc allows unlimited usage of the phone, it's called the honor system, you trust her to not use the phone after 10pm, long as her grades are good, she keeps possession of the phone 24/7, you can quickly check the only usage each day of the account (or weekly) and see if any calls were made after 10pm, and if so, take the phone at 10pm and return it in the morning, and put a land line in her room for the emergency use

again, just my 2 cents worth