In this paper we present an analytical model for the performance evaluation of GSM/GPRS cells with different resource allocation schemes. The presented model is based on the Modified Engset Model with a finite number of users generating ON/OFF sessions in the cell. The closed formula following from the model is applicable for calculating different performance parameters like user throughput, blocking probability and radio resource utilization. Our study is focused on two main radio resource allocation strategies: Complete Partitioning and Partial Sharing.