How will Facebook monetize WhatsApp?

Now that they have spent billions on it, what do you think would be their monetization strategy to make it worth the money spent?

I own stock in FB and feel shareholders should know some part of the long term strategy, especially with over 10% of the company's net worth was spent without a vote.

My opinion is that it was more to hedge any risk of competition with Facebook. FB's messenger wasn't even close to having the usage that WhatsApp has.

That poses a potential threat to Facebook. Zuck is willing to shell absurd amounts to not end up like MySpace.

I think FB can generate a good amount of revenue from having a WhatsApp for Business. Another could be simply to raise the $1 / year fee (which seems unlikely).

I don't think monetization was the main factor FB buying them.