Poder Local 2008/09 : quem é quem? / ed. Diário de Notícias
United Kingdom Telecommunications Report [documento electrónico] / ed. Business Monitor International
Facts & figures [documento electrónico] : about European Telecoms Operators / European Telecommunication Network Operators'Association
Voice [documento electrónico] : a vision of the future - Europe update / Mike Cansfield, Marta Munoz Mendez-Villamil, Mark Giles