If WhatsApp can ultimately generate $1 billion per year in net income, it's worth ~$19 billion.
It's extremely likely they can do that, if they can hold their market position. The business itself is capable of being very profitable over time, and has an extraordinarily low per user cost to operate.
It's not likely WhatsApp will ever be a wildly profitable purchase for Facebook, but it doesn't need to be. Half the point was to eat a rival, the same reason they bought Instagram.
The likely worst case scenario right now, outside of WhatsApp imploding, is that Facebook overpaid by 1x. To grab a billion users, and fend off a huge potential threat, that's easily worth single digit billions of dollars to Facebook.
To summarize Marc Andreesen: When I heard about the Whats App deal, I thought, wow it's worth that much. That must be what it's worth. Should I believe someone on the internet, or Mark Zuckerberg, who had painstakingly researched it, has access to the real financials and bet his own money and the future of his company on it.
I don't know about that; the phone numbers of 600 million users ( and rising ) tied to their identity opens-up the possiblity of correlating geographic graph data.
For example, Joe with a Chicago phone number has six Seattle area-code contacts. That looks like a marketable opportunity, why not advertise him some flights from O'Hare to Sea-Tac?
