The addition gives WhatsApp an answer to rivals that have had the option for a while, like Skype. And it's arguably overdue. Over 1.5 billion people use WhatsApp every month, with some of them relying on it as their primary means of phone-based communication. This opens the door to group video calls for a significant chunk of that group, many of whom might have trouble convincing friends to switch apps just for the sake of a face-to-face conversation.