See this discussion: http://www.quora.com/WhatsApp-Messenger/How-much-revenue-is-...
$20M net revenue, at most, right? With future expansion and side commercial services, I make $1B per year, fine. But that's after tax. So WhatsApp must make A LOT more than $1B. I really don't see anything else. But that's only when WhatsApp can continue to grow and actually gain that much of commercial income. Someone who have dealt with acquisition tells me how 16B is the right number. I would pay $5B just because WhatsApp is well-established.