This paper addresses the design and engineering problem related to mobile data services. The aim of the research is to inform and advise mobile service design and engineering by looking at this issue from a rigorous and holistic perspective. To this aim, this paper develops an ontology based on business model thinking. The developed ontology identifies four primary dimensions in designing business models of mobile data services: value proposition, value network, value architecture, and value finance. Within these dimensions, 15 key design concepts are identified along with their interrelationships and rules in the telecommunication service business model domain and unambiguous semantics are produced. The developed ontology is of value to academics and practitioners alike, particularly those interested in strategic-oriented IS/IT and business developments in telecommunications. Employing the developed ontology would systemize mobile service engineering functions and make them more manageable, effective, and creative. The research approach to building the mobile service business model ontology essentially follows the design science paradigm. Within this paradigm, we incorporate a number of different research methods, so the employed methodology might be better characterized as a pluralist approach.