[gregcohn]

I wrote about this a while back. https://medium.com/@gregcohn/burners-dont-hack-uber-people-d...

TL;DR Phone numbers are not unique ID keys for people. But it seems like many companies view it as an easy, cheap 2nd factor (generally, "something you have"), to be combined with a strong password ("something you know").

The problem of course being that SIM-bound number can be hacked or stolen, and non-SIM-bound numbers are not actually "something you have". If a Google Voice number is controlled by the same login as a gmail account, there goes your 2nd factor.

A lot of people do use Burner for this per the link above. (I'm a founder).