Mashups are getting more complex with the addition of rich-media and real-time services. The new research challenges will be how to guarantee the quality of the aggregated services and how to share them in a collaborative manner. This paper presents a metadata-based mashup framework in Next Generation Wireless Network (NGWN), which guarantees the quality and supports social interactions. In contrast to existing quality-assured approaches, the proposed mashup model addresses the quality management issue from a new perspective through defining the Quality of Service (QoS) metadata into two levels: fidelity (user perspective) and modality (application perspective). The quality is assured from quality-aware service selection and quality-adaptable service delivery. Furthermore, the mashup model is extended for users to annotate services collaboratively. The annotation occurs in two ways, social tagging (e.g., rating and comments), and QoS attributes (e.g., device type and access network etc.). In order to apply this network-independent metadata model into NGWN architecture, we further introduce a new entity named Multimedia Mashup Engine (MME) which enables seamlessly access to the services and Adaptation Decision Taking (ADT). Finally, our prototype system and the simulation results demonstrate the performance of the proposed work.