A 10 year old? No messages, pre-recorded numbers only - home, school, relatives, neighbour, and the like. In the U.K., all phones with a valid telephone number must be able to dial the emergency services, even if otherwise disabled.
I’d go with a pre-paid plan. I have the AT&T “pick your plan” and it’s worked out so far. If the phone is lost, you’re going to be SOL, but if it’s only broken and the SIM chip is good, you can get a refurb phone pretty cheaply.
Everything she does will go against a fixed dollar balance, so if the money runs out, you can put more on, but it’ll still limit her activities to whatever money she’s got.
If the money runs out, she’ll still be able to contact 911, but not family members. But I think this would be a good lesson in allocation of resources.
Dunno about all companies, but like with the T-Mobile family plan stuff, you can limit the number of minutes that the kid can use. I think with some plans for some companies also allow you to check on-line to see what numbers the child has called, but I may be wrong about that.
I’d agree with NO TEXTING unless you either think that you can trust your child not to be a textaholic, or you have unlimited texting on your plan. And then maybe too if you’re the kind of parent who is capable of setting rules and boundaries and actually enforcing them - for like taking the phone away if the kid gets caught texting in class.
Then there’s the whole “will the child lose the phone?”, “will the child break the phone?” thing. How careless is your kid? How expensive is the phone? Do you want to be constantly replacing it and dealing with the cell phone company because your kid leaves it in school, drops it in the playground, has it stolen or is constantly dropping it?