According to the Ministry of Information and Communications in Vietnam, as of November 2015, the number of mobile subscribers is over 120 million ones, accounting for over 86% of the total number of telephone subscribers. With a total population of over 92 million Vietnam citizens, a stable national economy and a large populations of young consumers in the country, mobile communication industries still have a huge potentials for future development. Telecommunication service providers in Vietnam are facing fierce competition. Subscribers are expecting OTT (Over the Top) applications, good quality service and handset subsidy. This study investigated whether legal frameworks, OTT applications, quality of service and handset subsidy are important components of mobile telecommunication service in Vietnam. This study used quantitative method to distribute surveys to mobile subscribers. Findings found that all four factors significantly influence mobile business in Vietnam. Thus, telecommunication service providers in Vietnam must continuously innovate to enhance operational competitiveness, improve business efficiency, expand business scale, and improve its position in the market in order to ensure sustainable development. Moreover, Vietnamese government needs to develop a legal framework to help mobile telecommunication service providers enhance the common interests and benefits of the entire society.