Oooh lucky DD! Mine only gets hand-me-downs. They treat them pretty rough... no way would I buy a new one for her. The less attractive it looks to potential thieves the better!
My DD often nags me for a new one but I keep telling her that while I am paying her school fees the only new phone she is getting will be my discarded phone when I get a new one.... and that will only happen when DH upgrades... that's how it works in our family: phones get handed down from person to person... starts with DH and ends with her (and probably her brothers too eventually)... means we only have to buy 1 new phone every 3/4 years. I hate to think how many mobile phones are lying around the planet which are in perfectly good working order yet discarded simply because it has ceased to flatter it's owner's ego. ie i refuse to allow a phone to be an expression of my fashion sense or that of my DD's. And that's my soapbox rant of the day... or at least the first!

ETA: I agree with Leasha, Prepaid is the ONLY way to go with a teen. I don't have prepaid on my phone but my bill is rarely over $25 a month.