We really need to go ahead and rip the band-aid off with the telephone network. "Even the small amount of meaning these digits used to have has been lost to time with cell phones and VoIP technology so any user can contact any other user appearing to be any rando with no authentication making the system rife for scams and fuckery and we have no plan to fix it. Participation is as mandatory as we can get without a constitutional amendment."
It's not quite as mandatory as it can get. The FCC has made rumbles about actually kicking carriers off the networks if they don't adhere to the shaken/stirred protocols, but never seems to get around to actually doing it.
Yeah I don't think it's actually illegal yet for a citizen to not have a phone number but try to get a job, go to school, pay your bills or be anything other than a wood chopping hermit without one. I'm a hermit but I heat my home with natural gas so I'm all but required to have a phone.