Does the price spent by Facebook for WhatsApp acquisition worth 19B$?

That's the question that all the analysts and press is keeping asking themselves..
And, of course, the answer is not easy at all.

Facebook today has reached an agreement with WhatsApp's founder in order to acquire the Messaging company for 19 billion dollars (4 of those in cash!).
But what actually Facebook bought is not the application itself (Facebook Messanger does more or less the same thing, and it's still in grow and used). What Mark Z. bought is users.

The WhatsApp customer base, to be precise, is composed by more than 450 milion contacts, 325 of those are active every day.
WhatsApp messaging traffic is equal to the entire worl'ds SMS traffic.
With an incredible success in the emerging markets like India, Brazil, Mexico, Nigeria and South Africa. Countries where Facebook usage is far lower than this.
The plan for the app will not change, It will continue to works with an annual subscribtion fee of .89$ and will remain advertising free.

So, it's this massive user base worth $19 billion?  Time will tell.