Next generation wireless networks must be able to coordinate services between heterogeneous networks through multi-mode mobile terminals. Such heterogeneity poses a challenge to seamless handover since each access network has different operations. In this paper, the policies of multiple metrics for handoff to permit connectivity across UMTS and WLAN/WiMAX are designed. Moreover, how to select an optimal target network is an important issue to balance against the network condition and user preference. The considered metrics for handoff initiation include the predicted Received Signal Strength (RSS) of neighbor networks and dwell time. The RSS is predicted by back propagation neural network which is beneficial to perform handoff early.