Re: "using people's cellphone numbers [...] to target them with adverts"
I still have an old Nokia 6310i (a lovely phone) that I've fitted with a PAYG sim card with £10 on it. I intend to use that phone if I ever have to set up 2FA by text for anything and it will only ever be turned on for that purpose.
(Also it has to be turned on at least every six months to make a call to my landline to keep the SIM card active. I don't have to pickup the landline for that to work. That's a calendar event with an alert to remind me every four months.)