The linked article also contains a link to the Apple Support site, which shows what sort of services are live across the various networks around the world. As of today, 25 networks in the USA and Canada have RCS active for iPhones. In Africa, it is zero right now, but Vodacom in South Africa said they were busy with it.
Basically, each iPhone user’s network must activate RCS for iPhones. Many already have RCS active for Android devices, but there is clearly some separate activation still required for iPhones.