Telegram solved this problem, they just sold a fake numbers on blockchain where you can get a number without leaving a trace and stay completely anonymous while keeping number-based model. Plus, additional monetization.
Edit: Just tried it again, and I cannot register on Linux without a phone number. Here is a screenshot: https://i.imgur.com/WcnHBx1.png
I wish signal did something similar.
Edit: find the numbers here: https://fragment.com/numbers
It's probably affiliated with Telegram, I'm not sure.
Yep, but it doesn't have to be a real, publicly routable one. You can get one from Telegram without having to provide government provided ID like I have to for real phone numbers. See sibling comment.