Earlier quoted context omitted.
I'm not sure how I feel about making it illegal, but it does benefit from some sort of collective action. If none of your child's friends and classmates have cell phones yet, I'd strongly encourage establishing a smartphone pact with the other parents. Our community used http://waituntil8th.org pledges but even a shared spreadsheet would work.
All that local level stuff doesn’t work. As soon as a couple of kids have a smartphone, the online world becomes vastly more interesting than the day to day.
I can't speak to anyone else, but it seems to be working well enough in our town. The overwhelming majority of kids don't have cell phones until high school. That doesn't mean your kids won't beg you for a smartphone, it just means you can say "no" without socially isolating them.
> As soon as a couple of kids have a smartphone
The point is to engage in collective action early enough that you can prevent these situations in the first place. Once a critical mass of kids have smartphones and their socialization and coordination moves to online spaces it becomes intensely isolating to be the only kid in a friend group without a smartphone.