Android

The confusion stems from the fact there no APIs in Android that let apps use RCS. Only Google can use it on Android and no other apps can use it. Anyone can make an SMS app. Only Google can make an RCS app.

It is an open standard, meaning you are free to create your own operating system for phones that implements RCS. But Google doesn't let you use it on Android, so in practice it's closed.

Plus, Google's implementation of RCS adds extra features (like encryption) that aren't part of the standard. So even if you create your own operating system that implements RCS, it will still be incompatible. So that's another reason it's not really open.

Yes, RCS is an open standard developed by the GSMA.

However Google has their own implementation of RCS.

It is an open standard. The end-to-end encryption is not an open standard, nor are the stickers, those are both proprietary to Google Messages but the rest is open.

Yes it is, it's been developed by the GSM Association, but Google does have de facto monopoly in the market right now by their ~~Jio~~ Jibe virtual carrier. RCS can be freely implemented by carriers and device manufacturers independently of that, but so far only Samsung, T-Mobile USA and Verizon did so — everyone else uses Google's Messages. Importantly, different RCS implementations can talk to each other, just like email servers, or Lemmy instances.

Apple has been encouraged to enable RCS compatibility in iMessage in a loud campaign by Google, but they are obviously not very eager to do that, as their own research shows the closedness of Apple ecosystem and messaging system is a main driving factor of sales. This has been revealed in the Apple vs Epic Games case hearings

It's kind of open. It's pretty much open for carriers to implement on the server side, and for OEMs to develop on the client side. There is an open source client in AOSP's RCS Test App, but for one reason or another, as far as I know nobody's attempted to implement it in an actual usable client app. I don't believe there's a server reference implementation. And, in the US, all the carriers' RCS services are run exclusively by Google, so there's no real point in attempting to set up your own server. Apple might be able to navigate the politics with carriers and with Google to make something work, if it wants to, but it's really not a standard for us to play with.

Use Matrix Instead.

Yeah, there are links to the standard on the Wikipedia page

It may be open as concerns specs, but in most countries you'll pay much for using provider services instead of internet.

On the other hand it's closed, because no one except big mobile comms can offer this service. It's better to avoid it. The only way to have free communication standards is to use the good old internet instead of the infrastructure of the provider.

No, not really