Until today, Facebook and WhatsApp probably have been best-of-category to some carriers/ phone manufacturers, but not must-have (or 'must-preload'). Of course, WhatsApp’s growth was partially led by OEM/ carrier deals. And carriers must have entertained the idea of forming some data tariffs with WhatsApp in lieu of losing SMS revenue. With or without it, WhatsApp grew exponentially to 450M active users as of today. Whereas Facebook Home with less than 5M installs total didn't get Facebook where they wanted to be- take over the home screen - even though Facebook too got a couple carriers support upon launching.
Now it’s more obvious that messaging and launcher (or combined) are the killer apps on mobile, at least Android, not only because they are the start & end points of users interacting with mobile but also they are in the forefront of distribution, as if OS for PC or search for browsers. Facebook probably wouldn't want to lose there.
Wearing my BD hat, Facebook could now bundle everything - Facebook, Facebook Messenger, Facebook Home, Instagram, and WhatsApp - and present to global carriers/ OEMs as 'take it all or leave deal,' similar to Google's revealed Mobile Application Distribution Agreement. That would be a lot more irresistible if any one of those apps is must-buy for your core target demo. To give some perspectives, if you want your phone to be the best/ most friction-less to share photos, you need to have a Facebook.
- Photos/day? Instagram: 35M Facebook: 350M SnapChat: 400M WhatsApp: 500M
I don't know whether ~$40 per MAU is the right price, but gaining such bargaining power as must-buy out of this acquisition would be priceless for the next couple years in working with OEMs/ carriers as OTT messaging takes over SMS completely and gets saturated soon. Furthermore, Facebook can certainly build more on top of the portfolio, such usual suspects include appstore as Kakao and/or LINE is trying to evolve, payment, or commerce. Time will tell…