(Note that kop316, who has the second comment there complaining about lack of MMS support, went on to implement MMS support themselves by writing mmsd-tng. Many distros added it recently and it supposedly should work with Phosh's Chatty and on SXMO.)
Yep, I wrote most of the support in for Chatty myself as well. Chatty works pretty well with MMS, and I have been using a Pinephone/Librem 5 full time for almost 2 months now.
