[declan]

>This is what I hate about apps and services using phone numbers as primary credentials. Phone numbers can and do change, so they're nowhere near as stable as e.g. a simple email address.

Well put. I can think of a half-dozen phone numbers I used to have that have presumably been reused. Though even email addresses can be reused: Yahoo announced in 2013 it was doing this.

From a HN app/service-development perspective, all of these approaches have tradeoffs. Facebook login gives you a scoped unique ID with a low probability of reuse (perhaps zero, I can't recall what the docs say), but some folks don't like logging in with FB or don't have a FB account at all.