I heard about RCS but this text was sent to my dad’s feature phoneThis is a function of RCS (Rich Communication Services). Basically its an enhancement to SMS. I haven't done much research on it so you'll need to Google it.
Its an upgrade to SMS basically. It gives users with Phones, Messaging Apps, and Carriers that support it (you need all 3) many features that we take for granted with iMessages. One of those features is read receipts. Verizon just released it baked into the functionality of the Pixel on Dec 6th..ish...
I don't believe the iPhone has full functionality of RCS but glancing around the web real quick does mention features like 'read receipts' can be implemented without full support. And to be honest, I doubt we will see full support because the message includes a executable portion which I find it unlikely Apple will implement due to security concerns. Need to wait and see and it should be easy to test.
This isn't restricted to smartphones. Features phones have had support baked into for a long time (like mentioned by another user).I heard about RCS but this text was sent to my dad’s feature phone