This paper presents a method to model the bit error rate in GSM, taking as inputs the carrier to interference ratio and the speed. The procedure is based on a characterisation of the bit error rate second order statistics. Then, a technique which allows matching of both probability distribution and auto-correlation functions is applied in order to obtain replicas of the bit error rate sequence. A method to obtain results for any carrier to interference ratio and speed is then proposed, based on linear interpolation. The results are compared to the output of the full transmission chain simulation, showing that a good degree of accuracy is achieved, while the simulation time is drastically reduced.