This is the closest I’ve been able to find - JMP which is used in Cheogram, a FOSS XMPP app, was working on it in May but I messaged them about it recently and there hasn’t been much development on it unfortunately. https://blog.jmp.chat/b/may-newsletter-2024

They allow you to have VOIP numbers and even a data only SIM with no KYC and pay in crypto if you want so it’s a pretty cool project overall. Maybe if more people message them about RCS it will become a higher priority.