Most kids had cell phones in mid late nineties where I lived, the phones themselves were cheap but using them were not very cheap, but giving a kid a phone so you could call them if the parent needed seemed popular.
So when talking about how many people have cell phones, the difference between "mid 90s" and "late 90s" makes a big difference :)
[1] https://en.wikipedia.org/wiki/List_of_best-selling_mobile_ph...
Other countries will have different specific times when this happened, but my impression is that cell phones largely took off in a lot of countries in the same way, because competition and high prices for spectrum meant the large telcos suddenly had a reason to poor vast amounts of cash into pushing cellphones almost "overnight", and suddenly even if you didn't have one yourself you'd at least know enough people that it wasn't anything unusual any more.
I'm 48. While I've seen many technical changes, and been part of e.g. driving internet adoption (the company I worked at in '95 was an internet service provide I co-founded, and triggered a price war on internet access in Norway with, that we soundly lost but at least it helped significantly change the market), but none of those changes - including the internet adoption - had such extremely rapid, very visible, effect on society in such a short period of time
(I think pervasive internet access has probably made a bigger difference in the long run, but of course part of that was also enabled by cellphones, but it took longer for it to shape things as visibly)
2) I graduated in the early '00s and I think maybe 5% of the kids in my graduating class, at most, had a cell phone by graduation. Mostly some shitty Nokia with a phone-only or low-texting plan (texting was still crazy-expensive), mainly for contacting parents about after school activity stuff.
Middle-class-spectrum car-dependent exurb. Maybe it was different for, like, kids growing up in Brooklyn or something? Or rich kids, perhaps.
A more-common perk for children of free-spending parents, in my town, was still a second POTS line, though I do think that was starting to tip the other way just at the end.
The US was far behind on mobile phones for a long time.