I've been a user of Google Fi for a few years now. I've also been a longtime user of Google Voice and Hangouts. Of late, I've been experimenting with Duo, Google's version of Skype meets Apple's Facetime. Like Skype, Duo let's you make outgoing calls, presenting your choice of numbers, much like Skype. Like Facetime you can make Duo to Duo calls without the chat.
Somewhere, Android Messages plays into this.
What I see is Google converging all the services, as they blend the OTT capabilities of Voice and Duo with the data centric service known as Fi.