The widespread diffusion of mobile computing along with the integration of telecommunication systems and the Internet enables a scenario where the promise of ubiquitous computing is starting to be realised. This scenario calls for novel services the can be deployed on-demand close to the user and customised to not only client needs, but also to the client current location. In particular, group membership management services should exploit the visibility of client location to organize effective solutions for group communication and interoperation and to promote the design and development of advanced collaborative applications, such as traffic management and e-care ones. The paper describes a middleware for group membership management (AGAPE) that exploits both the visibility of users position and the heterogeneous characteristics of the access terminals to facilitate interoperation in a pervasive computing scenario.