Gmail call phone feature seems to be available for several Gmail users. Once you install the video and voice chat feature from #-Link-Snipped-# , you will have the "Call Phone" option in your Gmail. Now, you will be able to make multiple calls with the tool. That is you will be able to dial and receive calls while you're already engaged in a call.
When you receive a new call, you can pause an existing call and resume the new call and switch between the calls. I'm yet to test the feature in my Gmail account. In case anyone's tried it, let us know how it works 😀