One of the common tools that support collaborative learning is web-based forum. A web forum is a place where students can ask questions, exchange their ideas, learning materials, learning experiences, and so on. As mobile devices can be used to access information from anywhere and at anytime, it would be useful to integrate these devices into such learning activities. However, it is a challenge to adapt web applications to mobile devices because of the limitations of screen size and processing power. In this paper, we introduce a novel application using mobile phones for accessing multimedia contents efficiently. Our system, the Interactive Multimedia Forum for Mobile Users (CoMobile), supports collaborative learning with various devices such as PC, PDA, and mobile phones.