When I have no choice, I use a free throwaway email service. Unfortunately it's much harder to get a throwaway phone number so it greatly annoys me when services (Twitter, specifically) require one

All of big tech is checking phone numbers against sophisticated databases to determine if it is possible for an individual to have that number associated with their cell phone device. If it isn't a real mobile number you are not getting in.

Where do these databases even get their data? IIRC the phone network is very opaque compared to IP addresses and internet routing.

Every carrier in canada and the USA sells this info for insultingly low prices.

CoD (or some similar game, sorry I don't keep up) won't even let you register with a prepaid phone number so there must be more granularity than it seems.

smspool, smspva, etc. not free but not expensive.