In this paper we describe an analytical model to compute the packet delay distribution in a cell of a wireless network operating according to the GSM/GPRS standard. GSM (Global System for Mobile communications) is the most widely deployed wireless telephony standard, and GPRS (Generalized Packet Radio Service) is the technology that is now available to integrate packet data services into GSM networks. By comparing the performance estimates produced by the analytical model against those generated by detailed simulation experiments, we show that the proposed modeling technique is quite accurate. In addition, we show that the results produced by the analytical model are extremely useful in the design and planning of a wireless voice and data network.