I believe even then only US carriers (the rest of the world has moved on from P2P SMS, and only businesses are really still sending them for SMS-OTP and marketing), and of course Google, as the only party actually invested in it (via their acquisition of Jibe [1]).

[1] https://jibe.google.com/

You can get access to send MMS though. RCS there is no one selling access yet, especially for person to person.

It seems people are, but not anyone with a big name: https://jibe.google.com/partners/messaging-partners/ I'm guessing it's provisioned this way. https://developers.google.com/business-communications/rcs-bu...

EDIT: https://github.com/android-rcs/rcsjta

Yes the Google Business stuff exists for B2C marketing type use cases, but it is a very limited feature set compared to real RCS and cannot be used for regular communications using phone numbers.

I believe GP's objection is to not being able to access RCS from a non-Google-provided app on Android, not access to the RCS network on the backend side.

Either might be useful but I'm actually more interested in the latter because I run a phone service