DD1 & DS1 were both given phones in the last year of primary school. Both on a plan, which we pay for, if they exceed the limit they pay the excess or lose the phone until it is paid. DD has only done it twice, and one of those occasions was only by about $10.
She did have to upgrade her phone because she lost it, and she paid for that herself. We have told her we will pay for her phone while she is in school, even though she is working now.