If you have a smartphone, you must be using LINE, KakaoTalk, or Whatsapp messaging app, if not all of them. But unlike KakaoTalk and Whatsapp, LINE also allows users to call other LINE users for free - great value-added service, isn't it!? Today I will explain more about LINE, its background story as well as how its developers use NoSQL together with an in-memory data storage to manage billions of user messages per month!