We had a prepaid "family cell" that the kids would borrow, as young as age nine (when my son started delivering papers on his own). He and his sister would take it, if they were going out for any length of time (ie, down to play in the park, off to the library, swimming with friends, etc). They got their own phones when they started high school, but again, they were pre-loaded. So, if the kids used up all their data, that was it for the month (no risk of emptying our account).
These days I tutor 8 to 12 year olds. Most have phones.
For me, it really comes down to how often you intend to allow your child out by themselves. If they are walking or biking to lessons by themselves, then it's a really good idea to give them a cell phone. I can't tell you how often I've had a student stare at me blankly when I ask if their parent is picking them up after class. At least the ones who have cells can text and ask. Otherwise, I don't know if the parent is running late or if I should send the child off by themselves.
I don't really see a phone as a big milestone or privilege. Just something that allows the kids to check in if their plans change, and which allows me to contact them if - for any reason - I'm not going to be where they expect me to be.
Does anyone else remember looking for a payphone to let your parent know you missed your bus? Or to ask if you can visit a friend? Changing my plans was a big deal, since I couldn't even go out without giving my mom an itinerary and contact numbers for the places I'd be. I remember having to ask in random shops and even bars, if I could use their phone. I also remember how upset and angry my mother would get, if she was trying to find me and couldn't, sitting at the phone, calling every one of my friends. I was so, SO grateful for cellphones, when my kids were young.