NHN Corp., South Korea\'s biggest Internet portal operator, said Thursday its social networking service has risen as one of the most popular applications for mobile devices in many Asian countries. Naver Japan Corp., a subsidiary of NHN, launched LINE in June as a free group messenger application for mobile phones, including iPhones and Google\'s Android-based phones. As of Tuesday, LINE ranked at the top of Apple Inc.\'s online application store in Hong Kong, Taiwan, Singapore and Malaysia as well as Japan, NHN officials said. Boosted by the growing number of users in Asia, including the Middle East, the total number of LINE downloads for both iPhone and Android phones exceeded 4 million four months after its launch. The company attributed the rapid growth to its unique features, such as a free call function and \"emoticons and stamps\", which add a personal touch to the user experience. Since those features were added to the application on Oct. 4, the number of users has skyrocketed, recording about 300,000 downloads per day, the officials said. NHN said it aims to make the service a top mobile messenger application in 108 countries worldwide.