Google is rolling out simpler video calling on mobile for Android users. Those wanting to make a video call will be able do so straight from the Phone, Contacts, and Android Messages apps. The integration is as tight as you’d expect (as seen in the GIF above) with the option to start video presented in the same list of options where you’d call or text a contact. Google says it will add a function later that allows you to upgrade an ongoing voice call to video with a single tap.
When the video call is made, it’ll be routed through your carrier’s ViLTE service (video over LTE). If you’re not on a carrier with that service, Google will link the call through its Duo app, as long as both parties have it installed. The integrated video calling feature is already rolling out to Pixel, Pixel 2, Android One, and Nexus phones. Google is working with carriers to make the feature available on other Android devices, but the company hasn’t given a specific timeline.
Source: https://www.theverge.com/2017/10/12/16463616/google-video-calling-android