Use viber without a phone number I don’t think so but what you an do is get a Google voice number and link that one to your Viber.  Viber will send a verification message to that Google Voice number.  I don’t think Viber will work without a phone number.   The application does not create an account and thus uses your phone number as your identity to allow you make free Viber call to your friends using their phone numbers.  Most of these social messaging apps require peoples numbers so they can match up your contacts list with users of their apps and even pull in images of the people to go along with your Contacts in the app.