Earlier quoted context omitted.
They didn't enforce payments. I remember they asked me money but the app still worked when I didn't pay. I was surprised, so when they asked me money again many months later I didn't pay again to see what happened. The app kept working. Months later they asked me money again and this time the app stopped working. But back then whatsapp was not as popular as it is now. I was still using SMSes with most of my contacts…
I wonder how many people paid anyway. Maybe their tactics would get enough payers to support the whole thing.
He further explained that it may sound somewhat counter-intuitive: the reason why they made the app paid for some users was to slow their growth (similar to Facebook's college-only focus) so they could properly build out infrastructure and improve on the user-experience [1].
[0] https://genius.com/Jim-goetz-jim-goetz-and-jan-koum-at-start...
[1] https://youtu.be/8-pJa11YvCs?list=PLQ-uHSnFig5OyY5JWSQrl_gES...