This work proposes a novel billing system model for voice call services on cellular networks, which includes the voice quality index estimated on the end user device as an additional parameter in the charging process. The solution proposed is focused on cellular networks, and the main goal is to improve the user's quality of experience (QoE) using the voice call service, because users pay according to their satisfaction level. Voice quality assessment tests were conducted, in which users evaluate different voice call qualities and fill a survey regarding the service costs. Results show how the service costs are correlated with the user' QoE. Furthermore, the solution network architecture is presented, which uses the mechanisms introduced in a 3GPP project named Minimization Drive Test. Also, the technical feasibility of the solution implementation in a commercial cellular network is demonstrated.