This paper describes a client-server speech translation platform designed for use at mobile terminals. Because terminals and servers are connected via a 3G public mobile phone networks, speech translation services are available at various places with thin client. This platform realizes hands-free communication and robustness for real use of speech translation in noisy environments. A microphone array and new noise suppression technique improves speech recognition performance, and a corpus-based approach enables wide coverage, robustness and portability to new languages and domains. The experimental result for evaluating the communicability of speakers of different languages shows that task completion rates using the speech translation system of 85% and 75% are achieved for Japanese- English and Japanese-Chinese, respectively. The system also has the ability to convey approximately one item of information per 2 utterances (one turn) on average for both Japanese-English and Japanese-Chinese in a task-oriented dialogue.