Future wireless networks will see a combination of 3G WWANs and WLANs, which provide data services at different rates and with different coverages. New handoff management schemes are required in such heterogeneous networks to ensure the continuation of application sessions with low handoff cost. This paper proposes a novel service-oriented vertical handoff scheme between 802.11b (WLAN) and CDMA2000 (3G cellular) which reduces unnecessary handoffs while providing quality-of-service (QoS) support for applications. Different handoff processes will be performed for different service types according to QoS requirements. The analytical and simulation results both show that the proposed scheme greatly improves handoff efficiency, provides a better handoff trigger, and reduces network overhead with low handoff latency.