Typically, studies of ubiquitous computing environments focus on context-aware assistance for activities in a closed domain, such as guide systems in museums, and ignore ways of coordinating services between two different service environments. However, it is important to provide them with personalized assistance services that seamlessly coordinate two service environments for the users who move from an open ubiquitous computing environment to other. This study specifically examines seamless personalized services for mobile users and presents a framework of rolebased agent coordination to provide services for them. In that framework, personal agents, which are always with the users, play roles assigned by a role manager agent when they participate in new environments. We show a new agent coordination protocol, which is an extension of the Contract-Net Protocol, to perform context-aware role assignments to realize those services.