After being announced and released in the Brazilian market last month, Google Duo now has the ability to make audio-only calls for all users worldwide starting today. The update is mostly a server side change but you will need to make sure you have the latest version of Duo installed on your phone. For reference, that is build 9.1.151636499. Once the update is on your Google account, you will have a toggle panel at the top of the display in the app where you can switch between video and audio calls. To place an audio only call, just tap the New call button and select who you want to call. As with video calls, the person you want to call must have Google Duo installed.
The addition of voice calls to Duo is a bit odd and, frankly, speaks to the ongoing confusion that Google has around their message apps and their roles. Duo was originally setup to be the video call app for consumers with Google Allo being the message app with Google Assistant built in. With the addition of voice calls to Duo, it is out of it original role a bit although you could argue it is still a real time communication event. Regardless of the logic, Google needs to clean up their messaging around their messaging & communication apps.
If you are not seeing the option to place audio calls within Duo, it could be that it hasn’t hit your account yet. Rollout is happening now but it could take several days before it hits everyone. So long
as you have the latest version of Duo installed, there isn’t more for you to do other than to wait for it to get to you.