I have gone back to using XMPP and have my family and friends using it. There has been a uptik in development of this protocol and the mobile apps have gotten way better. Facebook, whats app, google, and countless others all started with XMPP/jabber and they all could talk to each other. That is until they walled them off to try and force everyone on to there app. Its so dumb that we had a federated chat system that was taking hold until the big tech players got involed and sucked up the users then turned off federation. Chat could and still can be like email if there is critical mass on one of these federated protocols so everyone will start useing it.

My phone number is run though my XMPP server, no matter what phone or computer I use I can access my phone number. Hell I could drop my phone plan all together, if I wanted to and just use wifi for calls. 90% of the time im connected to wifi anyways. I use jmp.chat and the android app cheogram you should check it out.