Hop a ride on the Seoul subway, and you'll find yourself surrounded by a horde of mobile phone users all wrapped up in a yellow-clad app known as Kakaotalk. KakaoTalk is South Korea's #1 mobile chat app; in western terms, it's Facebook, Twitter, and iMessage all rolled into one. It's so pervasive, even U.S. President Barack Obama mentioned it on an official visit in March 2012 (a sound clip which promptly became a KakaoTalk ringtone).

 

As KakaoTalk's fan base continues to grow internationally, I considered one challenge that might eventually confront users: when your contacts live all over the world, it's not always easy to tell when your friends are available to chat, due to time zones. So I envisioned a feature, called KakaoClock, that solves this problem by indicating which of your buddies are "up" for KaTalking when you are.

 

While KakaoClock adds exrta functionality to the KakaoTalk app, it does so within the existing limitations of the app's current design. Below is the imagined user experience.