This paper analyzes the impact of the change in telecommunication regulation changes including the unification of telecommunication service on network investment. The unification of telecommunication service plays a role of separating behavior regulation from entrance regulation and reducing entrance constraints. Therefore, it is expected that the market spillover effect is high through the improvement of behavior regulation. In addition, the effects of the other regulation changes in the 2010 Telecommunications Business Act revision are analyzed. This paper discusses critical factors affecting the decision making process in respect to the firm level and analyzes the impact path guiding investment and innovation. The key findings are as follows. First, the impact of entrance deregulation depends on the intensity of deregulation. If the intensity is not high, this regulation increases the incentive on investment and innovation. However, if the intensity is high as shown in abolishing of licensing, it affects the incentive negatively. Second, if interconnection regulation focuses on existing facilities or the intensity is not strong, this light handed regulation might increase investment and innovation. However, if interconnection obligation is expanded to the facility not constructed or the facility applying new technology, this regulation might deteriorate investment. Third, price deregulation increases the competition of service but it also increases the business opportunity, which means positive effect on investment. Finally, the paper proposes the guideline for telecommunications policy.