Earlier quoted context omitted.
Frankly, I'd rather have a messaging system controlled by carriers but distributed among all of them (like SMS and RCS) than a messaging system fully controlled by a single company like Whatsapp, Telegram, Allo, iMessages and so on. I can still switch carriers and be able to communicate with my friends. The only issue I have with SMS is that it costs money when I'm not in my home country.
Re. being able to switch carriers and still communicate, what happens when you travel and (temporarily) get a local SIM? Are you suddenly messaging all your existing contacts from an unrecognized foreign number "Hi, it's John, this is my temporary Thai number..." and then relying on that message not getting binned by some spam algorithm? What prevents carriers from charging extra for RCS messages originating abroad?
Travel is an issue yes, but I think it's worth it to have a truly decentralized system.