Although Wireless Local Area Network (WLAN) services are inexpensive and have a high bandwidth, UMTS services provide a larger covered area and high mobility. Based on intelligent deduction, this study presents a novel service scheduling scheme for WLAN/UMTS dual-mode networks. The developed system, Distributed Multi-Agent System (DMAS), consists of a set of problem-solving agents that autonomously process their own tasks and interoperate with each other by a shared database to reach a suitable schedule for dual-mode network services. A two-level control mechanism composed of local-control and meta-control is proposed to achieve a high degree of goodness in service scheduling. Simulation results indicate that the quality of service (QoS) of the proposed discipline in terms of average delay and jitter is better than that of the pure UMTS network by 25% and 10%, respectively. The scheduling discipline can improve the service quality in multiple-mode networks.