It's ok for 8 year olds to have phones I reckon, maybe like a 10 quid handset though with a fivers credit a month. Just a way for them to get hold of you if they need to. I can't remember being 8 but they start going round freinds houses and stuff by then yeah?
If they want a decent phone, get a paper round and go and earn it though, no free rides. Maybe a couple of quid for doing a weeks washing up or something, mowing lawns for the neighbours, whatever. But I think it's important to let kids know that whatever they want in life they must go out and earn themselves. Reliance on parents clouds motivation to go places in life.