This paper is a contribution to the generic problem of having a simple and accurate analytical model to dimension GSM/(E)GPRS radio cells where voice and data traffic are mixed. Radio resources are assumed to be shared according to the so-called Partial Partitioning scheme where some channels are dedicated to voice, others to data, and the remaining are shared by voice and data. Voice has a total preemption priority over data on the shared part. This work shows how to calibrate an Erlang-like law based on Markovian modeling for this complex sharing resource situation and to validate it against real data. We present a complete validation framework on a live network for a simple and efficient GSM/(E)GPRS analytical tool.