The traditional approach to developing middleware platforms is to adopt a 'black box' philosophy whereby the platform offers a fixed programming model to applications together with a fixed per-platform implementation. In this paper we describe research which is exploring an open approach to middleware implementation. Our motivation is to accommodate the demanding requirements for quality of service adaptation which are imposed by mobile multimedia applications. We use an extended CORBA computational model which supports the concept of explicit open bindings which provide an architectural framework for openness and quality of service adaptation. The paper offers examples of the programming style facilitated by our architecture and reports on our implementation experience to date.