As anyone who’s worked with Mark Zuckerberg can attest, Facebook is always his preferred communication app. Brendan Iribe, the CEO of the virtual-reality headset maker, didn’t have the Facebook or Messenger apps installed on his phone. So Iribe suggested they use WhatsApp instead. Their conversations began just after Facebook announced its $19 billion acquisition of the company, and Iribe figured Zuckerberg might as well try to get his money’s worth.