Free Voice Call” icon appears next to your Facebook contacts in the iOS and Android Facebook Messenger app. Facebook has updated their Messenger app that includes the ability to make free voice calls to your online pals. Facebook may leave other popular free calling apps, such as Viber, Line, Google’s Hangout, Skype behind. As expected, Facebook Calling service is not Encrypted at all and efforts of NSA and Edward Snowden’s revelations realize all of us that there is no such thing as ‘Privacy’
Source: https://thehackernews.com/2014/04/facebook-added-free-voice-calling.html