The diffusion of smart devices has greatly influenced the market dynamics of the telecommunications industry. The competition paradigm has shifted from individual firm-based competition to ecosystem-based competition. To satisfy the diverse needs of market customers, it has become more important for telecommunications companies to form alliances with complementary partners in the ecosystem. This study empirically investigates the influence of ecosystem-based alliance formations on the financial performance of firms in the Korean telecommunications market. Specifically, the impact of a CPND (Content, Platforms, Networks, and Devices) alliance in the ICT (Information and Communications Technology) sector on firms’ profitability is examined using a structural equation model. The results indicate that before the diffusion of smart devices, ecosystem-based alliance formations with other firms in the ICT ecosystem were not effective for enhancing profitability. However, after this diffusion, alliance formation between members of the value chain in the ICT ecosystem contributed significantly to firms’ financial performance. This implies that recent alliances with firms that are constituents of the ICT ecosystem are an important element of profit generation in the ICT market in Korea.