how does viber make money?

it has a huge user base and but does it make money without charging them. ANSWER TO THE ABOVE QUESTION Companies with good user Base can always count on a Big players buying them just like the case of instagram or Skype. I guess it is this option that makes them go ahead with their business model and also brings in the Investors. If they succeed in monetising like facebook, it great news for them, else sell it off to interested parties.