In this paper we propose an efficient method for perceptual evaluation of speech quality in Universal Mobile Telecommunication System (UMTS). With this method, the network operators are no longer limited to the narrow set of tested system parameters available in the standards. Instead, they can modify system parameters to what they desire, e.g. different Frame Erasure Rates (FER), and the resulting impact on speech quality can be evaluated in a fraction of time as compared with corresponding subjective listening tests. An example case study where the system FER is allowed to increase to 10% is presented.