When Facebook hit 1 billion users in 2012, CEO Mark Zuckerberg said that when it comes to getting another billion users, “The big thing is obviously going to be mobile.” In an interview at the time, Zuckerberg told Bloomberg, “As more phones become smartphones, it’s just this massive opportunity.” Clearly, he was correct. A recent survey from Global System for Mobile Communications Association Intelligence (GSMA), the research wing of a U.K.-based organization that represents mobile operators ar...