We have developed a communication support system that estimates the situation of a person using schedule information and location information provided by a PHS (Personal Handy Phone System). From the lessons provided by our prior studies and inventions, we developed a new mobile communication tool for cellular phones that uses location information and schedule information. This is a kind of dynamic telephone book, which we have named iCAMS. We performed user studies for eight weeks in Tokyo with a group of students and with a group of small-office workers. By analyzing the communication logs, questionnaires and interviews we conducted with the users, we evaluated our system.