Thankfully, there are numerous reports that RCS works on Android devices in the U.S. and that it works on AT&T, Verizon, T-Mobile, and Sprint devices. Android users in other parts of the world can also use this trick according to a report from 9to5Google. To enable RCS, users must have an app that can see Android activities, the latest beta version 5.2 of the Messages app, and WiFi must be turned off. With those requirements met, the steps are as follows:
After following those steps, the user should see a prompt to turn on RCS in the official client. All four major carriers announced a cross-carrier messaging initiative that is based on RCS that will work across carriers around the world. The carriers expect to offer more details closer to the launch of the new CCMI or Cross-Carrier Messaging Initiative in 2020. It would be no surprise if Google kills off the "unofficial" ability to activate RCS.