> Assuming your carrier bothers to run RCS, the protocol works just like MMS and SMS do. If your operator doesn't peer with other operators then you'll have the same issues getting any kind of multimedia delivered from phone to phone.

Except, SMS/MMS can be implemented by any standard IMS stack and it will function on any carrier (in theory, ignoring implementation bugs/incompatibility);

RCS has an explicit provision in the standard for "client authenticity" checks which in practice means App Attest/Play Integrity signatures.

(see also: my comment above)

> And why is that? Assuming your carrier bothers to run RCS, the protocol works just like MMS and SMS do.

Correct. And it took more than a decade to get MMSC interoperability. It's still not perfect even now.

And mobile network operators were incentivized to enable MMSC peering because it was typically a pay-per-message service with hefty fees.

> Annoying, though hardly unexpected at this point. Still, that only poses a problem for Google's RCS servers, not for RCS itself.

That's a distinction without difference in the US.

> And it took more than a decade to get MMSC interoperability. It's still not perfect even now.

That's an understatement, my carrier has disabled MMS years ago. Still, that's not an issue with the MMS protocol, just an issue with carriers.

> That's a distinction without difference in the US.

The American carriers including Jibe in their network still speak RCS to clients. Google's Jibe is the most prevalent remaining RCS server but carrier Jibe isn't using the proprietary protocol that Google Messages uses (otherwise it wouldn't work on iPhones).

Looking at https://support.apple.com/en-us/108048, https://support.apple.com/en-us/118609, and https://support.apple.com/en-us/109526, carrier-based RCS is available in quite a few places. Nowhere near as prevalent as SMS/MMS hubs once were, but that has to do with the fact that in many countries SMS and MMS have been replaced by third-party apps over a decade ago.

> That's an understatement, my carrier has disabled MMS years ago. Still, that's not an issue with the MMS protocol, just an issue with carriers.

If a protocol requires something specific from carriers, then it's an issue with the protocol.

> The American carriers including Jibe in their network still speak RCS to clients.

Sure, and? It's still useless for me because it can't be used without Google Play.

US and about 180 other countries too.

RCS networks outside Jibe:

- China

- South Korea

- Japan with +Message, on its way out for Jibe

- Jio in India (very strange case as Android subscribers can use Google Messages on Jibe)

Global RCS == Jibe.

Google killed off all interconnected hubs.