The evolution of an “ open” communications universe is now expanding to deliver new communications services,characterised by advanced and ubiquitous,multimedia capabilities.The move by telecommunication companies’corporate customers into the IP world and the need for interoperability between private and public networks will drive service providers and telecom operators to adopt IP in their core networks as a means of unifying traffic types.The particular case addressed in this paper considers a complex yet realistic scenario:the convergence of Fixed/Mobile Communications Provider and Internet Service Provider through the transition to IP technology.