I went down the rabbit hole of trying to work out what this is. In involves new coins and ICOs. I'll stick with Matrix and Signal.

"Session is enabled by services provided through the Loki blockchain network. The Loki cryptocurrency is a fundamental part of these services, providing an anonymous way to transfer value between people. A lightweight wallet integrated into the Session app, using keys derived from the users existing keypair, could allow users to quickly and privately transfer value inside Session."

I think not being tied to phone numbers is on Signal's roadmap? Isn't that why they're encouraging me to memorize this PIN with spaced repetition? Or something?