It's unfortunate that RCS is basically a de-facto Google walled garden in most countries. On android you can only use RCS in the Google Messages app and trying to build your own is explicitly blocked. [1] And of course the bonus that rooted devices are banned from RCS. All the propaganda Google spread to get Apple onboard (only with Google's blessing of course, Google could kick apple off if they wanted) was such a big win for them.

As a business I wanted RCS to be a simple upgrade to SMS, but instead they came up with this mess. Businesses using RCS for Business can send messages to anyone, but customers wanting to get in touch with your business can't. They can only reply to a message you sent first. And of course Google is the gatekeeper for anyone to be allowed to use it.

1. https://github.com/microg/GmsCore/issues/2994

Unfortunately, I think what a lot of people don't know is that RCS actually has "client authenticity verification"[1]... the RCS server has to actively approve any attempts for a client to connect, if it's Android/iOS/etc.

There are no standards for how this should be implemented, Google uses Play Integrity and Apple uses App Attest at the current moment, with explicit proprietary support by the Jibe servers.

It's basically impossible for any solution that Google doesn't approve to function, because it's never going to be able to get App Attest/Play Integrity verification without relying on a jailbreak/vulnerability.

1. https://www.gsma.com/solutions-and-impact/technologies/netwo...

> Businesses using RCS for Business can send messages to anyone, but customers wanting to get in touch with your business can't.

Basically for blasting spam and ads, which RCS is already notorious for.

> trying to build your own is explicitly blocked

Google doesn't offer an RCS API, but making your own API is not blocked, especially not on phones running MicroG.

For standard ROMs, RCS apps are not feasible because carriers expect interaction with the SIM module, and only privileged apps can do that. Google Messages blocks root access (probably because the RCS spec says they have to if they ever implement the money exchange feature for RCS) but that just locks out Google Messages.

LineageOS, GrapheneOS, /e/, and all the others could build their own RCS client. They may not be able to register with Google, but they can make an RCS app nonetheless. Rooted devices can also promote third party RCS apps to gain system permissions, so they would be able to use the same RCS apps. Thing is, like all telco protocols, RCS is a long spec with a billion features and acronyms made up of acronyms of even more acronyms, plus you can't easily set up your own server (though in theory a sister project for an open RCS server might be useful for the open 5G project).

I get why people want Google to just stuff their RCS library into open source Android the same way they do SMS/MMS, but to say it's impossible to write a client for, especially when running at the permission level MicroG runs at, is not the whole truth.

As for the whole "Google is the gatekeeper" thing: there are more RCS-for-business providers out there. Google's is probably the easiest to use by far, but Twilio has RCS too, as well as smaller companies such as LINK Mobility and Esendex. Sure, the people whose carriers don't support RCS might receive these business messages through Google's servers, but there's no need to pay Google a dime to make use of the RCS for Business specs.

> customers wanting to get in touch with your business can't Not technically true, though it can be more difficult. It's similar to how Apple Messages for Business works where you have to be given a URL (or QR code) to start a conversation with a business using RCS.

to your point i had problems with RCS in an entire organization because you must allow *.goog for rcs to work correctly