Advances in high quality digital wireless networks and differentiated services have enabled the development of mobile multimedia applications that can execute in global infrastructures. In this paper, we introduce a novel approach to supporting mobile multimedia services by effectively exploiting the intermittently available idle computing, storage and communication resources in a Grid infrastructure. Specifically, we develop efficient resource discovery policies that can ensure continuous access to information sources and maintain application Quality-of-Service (QoS) requirements, e.g. required network transmission bandwidth on the mobile clients. Our performance studies indicate that mobility patterns obtained via tracking or user-supplied itineraries assist in optimizing resource allocation. The proposed policies are also resilient to dynamic changes in the availability of grid resources.