In Car Information Service Systems (Car Telematics), Speech Dialog Interfaces are important from safety viewpoints. However, there are many technical problems such as flexible dialog management, robust task management, and intelligent user assistance. We have proposed the CAMMIA (Conversational Agent for Multimedia and Mobile Information Access) to solve these technical problem. In this paper, we propose robust dialog management strategy and system architecture consisting of a Dialog Management and a Task Management, separately. Finally, we report the system evaluation results to confirm effectiveness of the proposed system architecture and dialog management for the mobile use.