United Kingdom was – alongside the United States – among the first countries to deregulate the telecommunications market in the early 1980s. Competition in the UK telecommunications started gradually about ten years earlier than in most other European countries. This paper traces the development of the corporate strategies of the incumbent, British Telecom, after the reform of the telecommunications market in the UK from the beginning of the 1980s. We explore how British Telecom utilised its early mover advantage when technological, institutional and competitive forces were shaping the telecommunications service industry in the 1980s and 1990s towards a competitive market. The paper illustrates the complexity and uncertainty that corporate strategists face in a fast changing environment. The paper suggests lessons for the telecommunications, media, and information technology service sectors, as well as the regulatory and institutional environment.