As it happened, I set up a new phone on AT&T this week and I was surprised to find that when I started Messages I saw a message saying Chat messaging was available. I then went in to Google Play and saw that the Carrier Services app was installed on the phone.
I still didn’t see the feature available on my Pixel 2, however, so I thought, what if I searched for Carrier Services in Google Play and tried to install it? Turns out that I found it and was able to install it and after that the Chat services connected and was functional.
I now have two phones with the feature enabled, which allows me to test it. You will know if you are using chat if you see “Chat message” displayed in the input box, otherwise you see “Text message”.
I find the chat functions similar to Facebook Messenger. If you are chatting back and forth you see the … indicating a response is being typed. The messages and pictures appear near instantly.
BTW, the two phones I have are on Android 10 and 9, so I know at least one generation older than the current will be able to use the service. I am looking forward to seeing whether/how soon my friends get the service.