There is a free voice and video chat option for use with Google Calendar!
Just create and embed the calendar widget to your page and add Google meet too it. Google meet is the new hangouts.
You get up to 1 hour of free video call a day I believe. So if you have a live event you are planning there you go.
Hope it helps! As an option you can also add bluejeans and other vid and voice apps through your calendar as well.