I got mine when I was 12 because my school was a bit far away and I had rehearsals and things that I needed to be picked up from at random times. It was a crappy hand-me-down thing - a Nokia of some kind - but I didn't mind. It did what it had to, and I hardly used it. I'm nearly 17 now, and I have my own phone on a texting plan, but I still barely use it. During the school year, I'll text one or both of my parents 1-3 times a day, and a couple of my friends maybe three times a week (I tend to Skype them from my computer). I don't call or take calls on it - as a matter of fact, the speaker's busted so I can't, but that's incidental - and I'm pretty sure I could manage without it if I had to. So like some others have said, it varies depending on the child. If they're out of the house and moving around a lot, I'd make sure they had one. If they were like me and just sat at home pretty much all day . . . no real need, I guess?
EDIT: Mum says she'll get my sister one when she's thirteen. She whines about it incessantly, though. Never mind the fact that she'd probably end up not using it . . . XD
