Thing is, it already was getting that adoption, and network effect can largely take care of the rest. Also, some it’s tied to a real phone number, geographic price differentiation is trivial to implement.
Ok I paid the 1 buck, or agreed to pay a year later. Those days I lived in India, and my friend kinda forced me to use whatsapp by selling it. I still remember sitting in an auto-rickshaw and downloading the app after the sales pitch :) This must have been 2012, but could it be earlier - maybe.
Point being, I agree with you, it was getting that adoption anyways, even with the fees. And within months, I was hearing this from so many others.
How do I remember? I moved back to US in Feb 2013, so it had to be before that, just can not recall the exact year and month.