The number of applications that use mobile devices in learning activities is increasing. The limitations of mobile devices such as small screen and inconvenient input facilities can be reduced by using multimedia contents. For example, students can submit questions by taking pictures of their notes; field trip experiences can be shared by video taken from mobile phones, and students can access long text information via voice instead of using SMS that allows only 160 characters per message. However, the use of multimedia information poses a new challenge for system developers: how can the students search on multimedia information? In this paper, we introduce a mobile-learning system that addresses this issue by applying several techniques such as Automatic Speech Recognition (ASR), Optical Character Recognition (OCR), and Text to Speech (TTS). The system is based on the CoMobile framework, our open source software framework for collaborative work using mobile devices.