Even though Google’s Home Hub lacks a video camera, it can still use the company’s video calling app, Duo.
The functionality, first noticed by Android Police, allows the smart display to use Duo but instead of taking part in a two-way video call, the user on the other end only sees a profile picture. Luckily, the user with the Home Hub will get to see the other caller.
Google’s Home Help page outlines the same information.
You can make and receive calls on your Smart Display if you have Duo video calling. Note: The device being used to contact your Google Home Hub must have a camera in order for the video calling feature to work.
Oddly enough, Home Hub can’t complete voice-only calls using Duo, which means Home Hub users can’t call one another; a smartphone or tablet with a built-in camera is needed.
Source: Android Police