When FB bought Whatsapp, Whatsapp was handling 20 billion messages a day and was the #1 app on the phone pretty much anywhere in the world, except for US, China, and Australia (it still is). Not that they needed some tool to find that out.
FB did an amazing job in keeping their acquisitions fairly independent and let them keep grow. That's something really hard to do and they deserve credit for that.
It is easy to buy the #1 messaging app in the world, if you have the money. It is hard to make sure those people still stay motivated after the acquisition.
WhatsApp's secret was that they struck deals with many operators world-wide to provide their messaging for free instead of counting it as Internet usage (look at Brazil for example). Not sure how did they achieve it but that for sure propelled them to #1 in many countries.
Considering how text messages and smartphone data usage have become far more popular than telephone calls, transmitting those messages via HTTP alongside other data traffic is probably cheaper than building out & maintaining a bunch of extra SMS infrastructure to handle the load.
FB did an amazing job in keeping their acquisitions fairly independent and let them keep grow. That's something really hard to do and they deserve credit for that.
It is easy to buy the #1 messaging app in the world, if you have the money. It is hard to make sure those people still stay motivated after the acquisition.