Due to mobile technology innovation in IT(information technology), the business on Mobile Virtual Network Operators(MVNOs) has emerged in mobile telecommunications service market. Considering technology innovation and its policy importance, this paper examines the competitive environments of mobile service business for MVNOs and the welfare effect of introduction of new mobile service. We first classify the service characteristics of MVNO and propose a mobile service differentiation model by taking the entry type of MVNO into consideration. We also analyze the welfare effect of mobile service business competition, depending upon the two specific entry types. In particular, we compare the mode of competition between simultaneous game of Full MVNOs and sequential game of Service Provider(SP) MVNOs, and suggest some policy implications on the efficiency of MVNOs competition in mobile telecommunications service market. Finally, we show that the entry type of MVNOs, the mode of competition