WhatsApp will soon make it possible to chat with people who use other messaging apps. It’s revealed some more details on how that will work.
— Apps will need to sign an agreement with Meta, then connect to its servers.
— Meta wants people to use the Signal Protocol, but also says other encryption protocols can be used if they can meet WhatsApp’s standards
— WhatsApp has been testing with Matrix in recent months, although nothing is agreed yet. Swiss app Threema says it won’t become interoperable
RCS should open up and let communities create their own apps.
From what I understand, it’s implemented on mobile carrier level, so any phone or other device with a cellular modem connected to a carrier that supports it should be able to use it (edit: of course, ignoring insufficient access, at the very least rooted Android or some Linux should work). Can’t really find more specific details right now though. Here’s a library and sample client for it though: https://github.com/Hirohumi/rust-rcs-client
Of course, this is only for clients, it’s true you can’t set up your own server.
It’s like with SMS, needs communication of the OS to the modem to the carrier’s server. And just like with anything carrier related the progress is very slow, no mobile phone even supports it (for now only Android with Google’s own app that connects to proxy to bypass the modem) and… is my opinion unnessesary.
Carriers already support it, and I think the reason Google sends it through their backend instead of the carrier’s is so they can support their proprietary extensions (that’s my guess at least, and I think I read that the app can also use carrier services directly but I can’t find the text that said that anymore). And as far as I’m concerned that means there are indeed many phones that support it.