The potential of mobile service innovations to create valuable economic impact makes their development desirable for companies. To develop and launch successful mobile services, the integration of customers in the idea generation process bears high potential. However, such Open Innovation activities usually demand for investments, whereas the precise relation between the money invested and the generated economic effect is still indistinct. The objective of this paper is to replace the black box between investments in Open Innovation and the thereby generated profits through formal-deductive analysis. For this purpose, we analyze the effect chain between Open Innovation and economic profit by adapting the model of Kano and putting special emphasis on the specifics of mobile services. Building on that, we develop a quantitative formal model to determine the optimal investment amount in Open Innovation activities for mobile services. The model’s utility is illustrated with an example based on real-world data.