The text messages we all used over the years are archaic and clunky, but RCS promises to modernize messaging with features like read receipts and file transfers. However, implementing RCS through the carriers has been an utter mess. Case in point: T-Mobile says the new Pixel 3a and 3a XL won't have RCS support on its network. We can safely assume the existing Pixel 3 and 3 XL (also now available from T-Mobile) will be the same.
You could understand the lack of RCS with previous Pixel phones on T-Mobile; it wasn't selling those directly. However, T-Mobile is now selling the Pixel phones, but it's not supporting RCS.
We're super excited for this device! No, the new Pixel devices won't support RCS messaging. Feel free to DM us any further questions. ^JamieEnglish
— T-Mobile Help (@TMobileHelp) May 7, 2019
Google has RCS support in its Messages app. That works fine for RCS on carriers like Verizon, but T-Mobile's RCS setup is still murky. It has rolled out support for the universal profile to phones like the Galaxy S7, S8, S9, Note 8, Note 9, and OnePlus 6T. We've reached out to T-Mobile for clarification and will update if we get more details.