Open innovation was conceptualised by Chesbrough (2003, p. 34) using cases from the ICT (Information and Communications Technologies) sector, more specifically equipment and component suppliers such as Lucent, IBM and Intel. Subsequently, the vast majority of the case studies in open innovation emphasised innovation processes in goods-based firms, not in service firms. Open systems innovation was well known in the telecommunications industry well before Chesbrough’s conceptualisation of open innovation. However, subsequent research has not paid much attention on its adoption by incumbent telecommunications operators. This paper investigates how open innovation was adopted by the incumbent telecommunications operator BT in the UK, using the case study as the research method. BT used open innovation as a management injunction to systematise innovation under a common framework to leverage and integrate technology and knowledge in order to address customer needs, and to change the way of thinking about innovation within BT.