No they aren't. Do they make life a hell of a lot easier? Yes, but you don't need a cellphone to live.
You need a cellphone for your boss to call you.
You need a phone. Not a cellphone
Cellphone service is cheaper than landlines in some areas, so certainly you're ok with cellphones in these areas?
If you need one for your job, yes. Picking up a little phone that's like $20 and you need to put minutes on it.
Problem is, the people who say they NEED a cellphone are the ones who are the people who have the $800+ phones. I have never met a person who said they absolutely must have one who didn't have a super expensive, top-tier phone.
Nobody gives a shit about your anecdotal experience dude get outta here with that