Basically an early version of Wi-Fi calling before Wi-Fi calling was a thing. You signed up for a SIM-free phone number tied to your Google account that allowed you to make calls as long as you had Internet. Calls between US numbers were totally free, even if the Google voice person was in a different country

Anyway, Google voice is still around and has an app. So if you have a Google voice number, you have a totally separate dialer and text message set up, that’s distinct from the one for your regular number. But, as I mentioned, the text message part still doesn’t support RCS. Pretty embarrassing for Google