While Messages and RCS is how Google wants you to message friends, Google Chat also fits that role and the company today reminded us...
tl;dr: after pushing rcs so hard for years, killing hangouts well after forgetting about it, & hiding it from gmail, google now wants you to use its (and google allo's) successor, google chat.
I always used to use allo and hangouts when I was a flight attendant as they would still send messages despite the airlines paywall for the internet on their wifi. no idea how it worked but was awesome little gimmic