Internet companies have utilized the benefits of open innovation and open APIs for a long time, but mobile operators are just entering the open domain with a concept referred to here as Open Telco. This paper investigates how open APIs can be applied to mobile networks in order to transform them from a one-sided into a two-sided platform where new business models can be utilized. The research method is based on a single case study using a representative usage scenario. The research framework, applied in this case study, was driven by the literature analysis. The research was started by creating a set of usage scenarios for analysis by an expert group. The most representative case was then selected for a closer examination with the results presented in accordance with the research framework. According to the results, the Open Telco concept creates an ecosystem that enables a two-sided platform. However, positive network effects require at least national coverage; developers want innovative pricing schema and novel payment services need changes for regulation. Finally, the research limitations are expressed, the proposals for the next steps are given, results are compared with the literature findings, and conclusions are drawn.