The increasing demand for broadband wireless service in today's wireless communications, especially with WiMAX technology being one of the 3G standards, is causing cellular network providers to consider the integration of different heterogeneous networks. Consequently, network selection techniques play a vital role in ensuring quality of service in heterogeneous networks. In this article we have developed a network selection scheme for an integrated 3G/WiMAX heterogeneous system. The design goal is to provide the user with the best available QoS at any time. The proposed algorithm selects network on the basis of available bandwidth estimation. Analysis of heterogeneous system with 3G and WiMAX network reveal that the proposed network selection method can effectively choose the suitable network by negotiating trade-offs among network dynamic condition and multimedia service application.