The data traffic in wireless networks for the third generation (3G) mobile telecommunication systems should take into account a variety of services (voice, data, video) and environments (e.g.: private, outdoors, indoors) as well as the user mobility behavior. A good evaluation of measures of performance can help a system designer to make its strategic decisions concerning cell size and the number of channel frequencies allocated to each cell. In this paper we present an analysis of data services in a third generation mobile telecommunication networks based on simulation. In addition, we illustrate the need for a simulation in order to characterize the mix of several traffic types for capacity and quality of service (QoS) planning. We use the distributions heavy tailed Weibull and Pareto to simulate respectively, the data traffic and the resource occupation time for data service. Finally, we also comment some simulation results of third generation services where we analyze the QoS parameters of a mobile network, such as channel occupation time, handoff, new call blocking probabilities and traffic in Erlangs.