The convergence of heterogeneous networks, such as cellular mobile systems, wireless local area networks and other wireless broadband systems, introduces an increasingly strong trend, to margin monolithic approaches in favor of more flexible architectures, leading to the so-called beyond 3G networks. This paper initially summarizes the generic requirements for beyond 3G radio systems and describes various relevant architectures. Special attention is given to issues relating to the QoS provisioning in such an environment. A service-based approach, used in the IST-CREDO project, aiming at simplifying QoS provisioning is described. A qualitative comparison of the aforementioned architectures, with special focus on the QoS provisioning issues and requirements from the underlying networks is given while conclusions are being drawn.