@PublicLewdness As I have heard, the Signal protocol (or whatever is the correct term) is used also by other chat sw. It does not meen all those can interact with each other, but that Signal protocol is very good beyond its own platform. I agree the phone number is a drawback for Signal (is there any good pro with that, or simply the solution they have used).
@PublicLewdness Aha, ok, not an obvious relation to me. A major advantage though as end user with the phone numbers, is the possibility to easily find which of my contacts that have Signal, so I eg can send a message by Signal instead of SMS. Phone numbers are generally public open catalog info, at least here in my part of the world.
The excuse for requiring a phone number from the Signal team I have heard is that it cuts down on spam. That is a weak excuse to me that regardless of it being true or not makes me avoid Signal.