A popular instant messaging (IM) app called Kakao Talk is being credited with keeping users in touch when Japan’s voice networks were struggling during the earthquake earlier this month, according to the Wall Street Journal. Launched in March last year, the free app (which was developed by a Korean firm also called Kakao) is a huge hit in Korea but has also gained an audience in foreign markets, including Japan. Kakao Talk has more than nine million users worldwide, with one million outside of its home market.