Ambient and pervasive technologies provide several ways to assist people with special needs in smart environments. However, the system's complexity and the size of the contextual information of these environments lead to several difficulties in deploying and providing the assistance services. A service provision mechanism which is aware of the environment context can simplify the deployment of assistance services on environment devices, by taking care of the decision processes. Moreover, the integration of the interaction modalities in the decision processes of such mechanisms allows deliveries of services to users based on their capabilities and preferences. In this paper, we present a context-aware service provision system for smart environment, which takes into account a whole set of contextual information: user profiles, device profiles, software profiles and environment topology. In regards to our previous work, this paper focuses on the modeling of the user interaction capabilities, built around the notion of interaction modalities. We also detail the integration of the model to the service provision reasoning process, as well as its implementation. Finally, we demonstrate the functionalities of this system through technical validations and scenarios carried out in a real smart apartment.