Does Pinephone use the same stuff that Purism has been building or is there a standalone SMS/MMS app now? It was always my impression that they've been piggybacking (and good!) but the progress rate from Purism leaves a lot to be desired. I was rather surprised they were building SMS/MMS stuff on top of libpurple, like I never considered the idea of using pidgin (technically Chatty for them) for text messaging even if it makes a sort of sense. Last I heard in March, MMS was so broken that if you even just received an MMS message, it would corrupt that contact and you couldn't send or receive anything anymore from them. One 'solution' at the time seemed to include trashing the .purple/chatty/db/ folder and restarting phosh. I know someone who has both phones so I've been hearing some fun stories of brokenness, but I've yet to receive my own librem.
PinePhone does nothing. The different software stacks are a different story. You can several different phone software stacks on the phone, one is Purism's and so of course it does, but I'm not sure about the other choices.