Work on PinePhones and Librem 5 is going well. There are still issues of course but I’ve been blown away by the community efforts to iron out the issues. You can get Linux Signal and you’d still need to have it connected to an android or iOS device too, but that would at least give you messaging.

The other caveat being that there are still many apps that are not designed for mobile form factor, and while there is strong work on libhandy and many apps use it for responsive GTK apps, there are many great apps were work hasn’t yet started for mobile sizing/touch input/virtual keyboard