Do service providers lock their tariffs to prevent overspending

[Faz]

Basically we're buying one of the kids a new phone for xmas, it works out cheaper to get it on contract but I'm concerned she will over use it.
Do any providers allow you to lock the tariff so she can't go crazy and run up huge bills.

Cheers Faz

 

[Faz]

Thanks for the replies, I'll look into an O2 contract, she's on O2 payg at the moment so I'll see about changing it to a contract

Kid + Contract phone = bad

I know that's what I was thinking , I honestly don't think she'd run up a bill on purpose but I can see it happening.