Mobile computing has been mainly utilized for point-to-point communication services, such as E-mail or FAX among people. To advance this field, the challenge is to encourage group communication by providing information that encourages community formation. As the first step towards this goal, we experimentally implemented the community viewer, which dynamically visualizes the communication interaction among people in the community. To design the community viewer, we introduced (1) the party room metaphor, which provides a virtual place for representing various community activities, and (2) the reflector icon, which reflects the activity of the corresponding individual while protecting his/her privacy. The static relationship among people and their dynamic activities are displayed in the spatial arrangement of reflector icons in the party room. We report our experiments on implementing and testing the community viewer in an international conference using 100 personal digital assistants.