People do pay for WhatsApp - the article says $1/yr although I think I paid 69p for life (approx $1) for the iphone app. If they get 1bn people paying $1 then that's a decent income. I was reluctant to pay - I'm tight like that - but I had to because my friends were on it and wanted to communicate. Though I note people are moving to Viber to some extent which is similar but free.