I agree that $1/yr would shove off majority of users off the app. That said, I think WhatsApp could get to revenues of $1-3B per year because of the following:

* I pay $60/mo for my AT&T line. I do the majority of my communication over WhatsApp. In that sense, WhatsApp adds more value to my life than AT&T. There are a group of users who'd be willing to pay more for that value.

* For most users, WhatsApp is an integral part of how they communicate with friends, family, doctors, coworkers, etc. As a consumer, it isn't just an "app" but an integral part of their communication flow.

* WhatsApp is respected by international telcos. I know at least for the telcos in my home country that they'd be happy to charge for WhatsApp subscription as part of their packages.

I think the primary problem was that even if WhatsApp could monetize $1-3/yr per user on average, it still wouldn't have met FB's revenue expectations.

WhatsApp relies on network effects to be successful. If you get less than 100% of users continuing to pay and use the product then the utility goes down; the paid product is actually worse than the free version.

I honestly believe the friction of paying any non-zero amount at all for a messenger app is more than what 80%+ of users would be willing to bear psychologically. They would almost certainly just migrate to a different app. That's also where WhatsApp's group emphasis becomes a huge drawback - groups would tend to migrate together, making it easier and quicker for the whole network to unravel.

But that's what WhatsApp was doing before.

No they were not. This is a complete falsehood. They sold the company well before they could roll out their monetization plan widely enough for it to impact user retention. They were also much smaller at the time.

Well, but WhatsApp proved you what, because that's exactly what they were doing for a while.