3G/WLAN dual-mode mobile communication service possesses global mobility and roaming with high transmission rate and low communication cost. However, it confronts the drawbacks of long call-origination delay, heavy vertical handoff (VHO) overhead, and unnecessary battery energy consumption. In this paper, we analyze the mobile and call patterns of users to identify the factors represented the condition of the visited communication environment. We also propose a simple mechanism for dual-mode mobile terminals to determine the network system to adopt to avoid the drawbacks. Our results show that the proposed mechanism can effectively alleviate call-origination delay and VHO overhead. Besides, the grade of service of WLANs in dual-mode environments is enhanced.