The customer base capture along with acquiring the best social graph available (people usually only message through cellphones to other people who they are truly connected, unlike the social media) was well worth 19B.
What use spending big on buying a large userbase if you don't monetize it?
I see a lot of trivial possibilities to monetize 2B+ users. You can either act on those possibilities now, or rely on the valuation to sell the company on. Sooner or later, someone will monetize, and that's what's important.
Right now in my "updates" tab i am proposed stuff like Real Madrid C.F (a while ago it was another team), WhatsApp itself, Juventus and Arsenal.
They're dumb as well, because I have no interest in football.
That's spam advertising, they're most definitely getting money out of that.