It's my understanding (Please correct me if I'm wrong) that RCS is technically an open standard set by GSMA, which goes through the carrier just like SMS/MMS, and that Google's implementation in the Google Messages app goes through their servers and has extra proprietry features like E2EE. How do these standards interact of they seem to work in different ways? With the announcement that RCS will be implemented in iOS 18, it seems that they are not using the proprietary Google implementation. (or are they?) Im struggling to find a conclusive answer as to whether RCS is a GSMA open standard through carriers, or a proprietary standard through Google servers. If it is an open standard, then why hasnt there been any progress in an open source implementation?