This article explores from a multidisciplinary and transnational historical approach the impact of technological change on the structure of the telephone sector, the fruit of advances in microelectronics and information technology. This problem has been studied in Spain basically by regulatory specialists, on the one hand, and technologists, on the other. We lack a more transversal analysis that puts into play the various elements that intervene. This article is intended to cover this gap, based on unpublished primary sources-primarily from Telefónica-as well as in other documents of diverse origin. Specifically, it focuses on the role played by Spain and the historic telephone company (Telefónica) in the transition to the third generation of mobile telephony (Universal Mobile Telecommunications System, UMTS) and gives prominence to the national state, to the supranational bodies-EU and International Telecommunication Union (ITU) and companies.