I just read the article and wasn't sure what RCS really was and still am not a 100% sure but it says here about Sprint which I copied and pasted below. I am on Sprint but getting unlocked so will I have it? I may have it now since I got my pie update on my 9 plus and just don't know about it how do I check? And then it said the other person has to have it in order for it to work.
Sprint
To Sprint's credit, the Now Network has actually been at the forefront of the RCS Chat rollout. All new Android phones on the carrier's network support RCS that is interoperable between all carriers, so long as you're using either Google's Android Messages app or the Samsung Messages app that comes pre-loaded on Galaxy devices.
Ideally, RCS should be enabled by default. If it isn't active on your device, check the Settings menu of either Android Messages or Samsung Messages, depending on which you use. Other third-party or device-specific texting apps are not yet supported.