Packet service models are important to the research on the performance of mobile communication systems, network layout and system evaluation. This paper analyzes the characteristics of the UMTS system with its singleuser service as a reference model .A wireless packet service model is built based on the behavior features of HTTP packet flows. We put forward a capacity dimensioning method for the network planning of 3G systems serving the data services in mobile wireless environments.It is indicated by an instance that the method can easily be implemented and numerically analyzed. The service model is described with finite state machines. It is conducive to wireless resource management and flow control.