The Signal messenger and protocol.

In the video, it sounds like the account will still be associated with a phone number, but users will be able to hide the number on Signal itself. Essentially creating a second on-platform identifier.

This would solve the expected spam problem that would occur if the phone number requirement were removed, and might protect against stalkers et al, but intuitively I'd say you could probably require Signal to reveal the phone number associated with a username. So it's probably not a step towards anonymity.

... anyway: super exciting and very welcome. Hopefully they will finally ship it. .... after hinting at it for several years.