I was working with RCS related stuff for a carrier R&D group in 2008-2009. I was sure it was a dead horse already then, so it blew my mind when the term reappeared a year or two ago. I actually had to check if it was just coincidentally the same name. But no, somehow the thing was still alive and now after over a decade actually adopted too.

It's anyway useless outside of US now as that ship has sailed, proprietary chat apps ate the market.