With the aim of providing a guideline for understanding the future diffusion pattern of mobile telephony service, this paper finds some factors which influence the market diffusion of the 2G mobile telephony service. Using the Bass diffusion model, this paper divides the whole diffusion process into three stages. And then, this paper uses an OLS regression model to identify the determinants of the market penetration rate of the 2G mobile telephony service for each divided stage. The empirical regression results underline the importance of the eight factors with regard to the acceleration effect on diffusion rates. This paper suggests that results found in each phases are different from those found in the whole diffusion process. Furthermore, comparing the results of each phase provides more comprehensive understanding about the factors in terms of the penetration of mobile telephony service. This paper suggests some important implications for policy makers and service providers in the OECD member countries and other developing countries. And limitations of this study which should be reconsidered in the future research are also presented in this paper.