The last years have seen an exponentially growing interest for mobile telecommunication services. As a consequence, a great diversity of applications is expected to be supported by cellular networks. To answer this ever increasing demand, the ITU-R defined the requirements that the fourth generation (4G) of mobile standards must fulfill. Today, two especially promising candidates for 4G stand out: WiMAX and LTE. However, 4G cellular networks are still far from being implemented, and the high deployment costs render over-provisioning out of question. We thus propose in this paper accurate and convenient analytical models well-suited for the complex dimensioning of these promising access networks. Our main interest is WiMAX, yet, we show how our models can be easily used to consider LTE cells since both technologies are based on OFDMA. Generic Markovian models are developed specifically for three service classes defined in the WiMAX standard: UGS, ertPS and BE, respectively corresponding to VoIP, VoIP with silence suppression and best-effort traffic. First, we consider cells carrying either UGS, ertPS or BE traffic. Three methods to combine the previous models are then proposed to assume both UGS and BE traffic in the studied cell. Finally, we provide a way to easily integrate the ertPS traffic and obtain a UGS/ertPS/BE model able to account for multiple traffic profiles in each service class while keeping an instantaneous resolution. The proposed models are compared in depth with realistic simulations that show their accuracy. Lastly, we demonstrate through different examples how our models can be used to answer dimensioning issues which would be intractable with simulations.