In this paper, we propose and analyze a service-dependent handoff and channel allocation scheme in voice and data integrated cellular mobile systems, which combines the ideas of “Variable Bandwidth” and “Preemptive Priority” together. In the scheme, voice and data traffic are considered. According to the variations of the offered traffic intensity at each cell, both a voice and a data call in service can occupy a full-rate channel or a half-rate channel. In order to guarantee the Quality of Service (QoS) for both voice and data traffic, channel resources are fairly shared between voice and data calls according to an optimal channel allocation scheme, which minimizes the difference between the average bandwidth of a voice call in service and that of a data call in service. To minimize the forced termination of a voice call, a voice call can preempt a data call in service if all the calls in the channel pool of the current cell are already assigned with half-rate service. The interrupted data call returns back to the queue specially prepared for data traffic. By analysis, we obtain the most important system performance measures. Comparisons with the scheme, which only supports “Preemptive Priority” without “Variable Bandwidth” supporting, shows that if the total arrival rate for originating calls is not very heavy, the new scheme can provide lower blocking probability and forced termination probability for both voice and data traffic, and shorter average total transmission time for a successfully completed data call.