Google Fi launches advanced messaging feature for compatible smartphones
You can think of it as an alternative to third-party messaging apps like WhatsApp, Facebook Messenger, and Viber, or the Android version of iPhone's iMessage. RCS messaging enables users to send messages as large as 8,000 characters, as opposed to the SMS limit of 160 characters.
There are already a couple of carriers in the United States that have already launched RCS support for some devices like the Verizon Pixel 3 and Pixel 3 XL, as well as T-Mobile Samsung Galaxy S7/S7 edge and Galaxy S8 Active.
Otherwise, you'll have to download Messages app from the Google Play Store and set it as your default messaging app. After the installation process is complete, you should receive some prompts to enable RCS.