A lot of people are missing the point, citing the income WhatsApp has to make for Facebook to make back the money.
What they forget is that WhatsApp was able to serve almost half a billion users with "minimal" hardware. That's what Facebook wants, Facebook will save a lot of money if they can be as efficient as WhatsApp in terms of hardware savings, engineer ratio user ratio. I would imagine that's Mark is aiming for.
They bought a massive customer base in developing countries, and they manage to secure all of those users who use a messaging app without probably doing any deals with any telcos.
Not only that, they gained a potential advantage in the payments space. Potentially turning their users into being able to make payments within the facebook & partners networks.
Look at what is happening in China with companies turning their chat apps into taxi booking apps like WeChat.
What they forget is that WhatsApp was able to serve almost half a billion users with "minimal" hardware. That's what Facebook wants, Facebook will save a lot of money if they can be as efficient as WhatsApp in terms of hardware savings, engineer ratio user ratio. I would imagine that's Mark is aiming for.