We analyze dynamic processes of diffusion of innovations of two information technologies, the 2G cellular phones and the access to Internet in Japan, within the framework ofeconomic theories, namely substitution, complementary, and independent effects betweenthese innovations.The empirical results indicate that rapid diffusion of the 2G cellularphones exerts a negative effect on the diffusion of internet access technology, therebysuggesting the substitution effect between them.We, however, argue that this should beconsidered as an outcome of the short term effect, and propose the long term strategy tostimulate diffusion of both of these technologies based on the diffusion theory.