WhatsApp’s Cofounder On How It Reached 1.3 Billion Users Without Losing Its Focus

Even under Facebook ownership, Jan Koum says that the simplicity and efficiency that made WhatsApp a hit in the first place remain all-important. Three and a half years ago, Facebook announced its plan to acquire messaging phenom WhatsApp for $19 billion—a price tag that was a head-snapper at the time, and remains one today. But it was only in January of this year that the WhatsApp team, which has worked out of a succession of Silicon Valley offices, moved onto the Facebook campus in Menlo Par...