The Librem 5 should support @matrix IM at launch. @Purism works with the @gnome community to split Fractal into two apps:
- GNOME Messages (for individual or small groups conversations, either through Matrix or SMS)
- GNOME Conversations (for larger channels)
There also is a PoC application being worked on in case E2EE is not supported in GNOME Messages/Conversations by the phone launch.
Other protocols (e.g. Signal) likely won't make it to GNOME Messages, at least initially.