QoS issues will play an important role for the success of Web services. With the increasing number of mobile devices consuming Web services, specific QoS mechanisms are required for the efficient use of Web services. We introduce our Web service QoS framework that is designed for QoS-aware service specification, discovery, selection, and invocation of Web services. Applying the framework enables cross-layer communication in order to achieve cross-layer QoS differentiation. We present an architecture based on this framework supporting mobile and wireless Web service clients.