Any single type of existing wireless and mobile network cannot provide all types of services, e.g., wide coverage and high bandwidth. An integrated wireless and mobile net- work is introduced by combining different types of networks to provide more comprehensive services. In an integrated wireless and mobile network, a mobile terminal equipped with heterogeneous network interfaces can connect to dif- ferent types of networks. Therefore, how to select a de- sired network is an important issue in the integrated wire- less and mobile network. Although some network selection strategies have been proposed, most of them are designed to meet users? needs, such as bandwidth, money cost, or power consumption. Also, the system performance has not been touched. In this paper, we propose a cost-function-based network selection (CFNS) strategy in an integrated wireless and mobile network from system?s perspective. We also an- alyze the system performance of the proposed strategy using theoretical model and simulations. The results show that the proposed network selection strategy affects multiple system parameters, which needs to be handled carefully.