We present a novel technique to combine services, provided by mobile as well as fixed devices, on-the-fly and in a context-sensitive way within smart environments containing groups of people. The key intuition at the base of our approach is that, in those environments, similar functions are provided simultaneously by many agents on board of different devices; the issue becomes then of combining and coordinating their services in order to exploit their aggregated power or improve delivery. At the core of our work is the idea of implicit organizations, that is, teams of agents that continuously renegotiate how to provide services while the environment evolves. A concept demonstrator shows how implicit organizations can support a smart virtual meeting room. We foresee the application of our approach in assisting users and groups of users in active environments, such as an active museum. Here, our approach can enhance knowledge transfer and communication for groups visiting together cultural exhibits.