Is internet required for Viber to work?

viber calls internet required

Yes, internet is required for Viber.  Viber makes calls and sends messages through the internet so you either got to have a Wi-Fi connection or a data connection (preferably 4g or LTE).  Viber is social messaging app like Snapchat and it is better than Skype in a lot of ways.  It offers better rates than Skype for international calls.