With over 400 million active monthly users, that would be much closer to $399,000,000 than $0.99 every year.

WhatsApp has nearly twice the active users as Twitter, and many more than Skype, LinkedIn, Instagram, and even Angry Birds.

Not only that, WhatsApp has a user:employee ratio of over 8,000,000:1. That is quite remarkable, over 8x the users per employee than Youtube.

There is much more value in WhatsApp for FB than just eyeballs.