This paper proposes the medium-long term vision where Telecommunications networks will evolve towards becoming Software Defined Infrastructures (SDI). In particular, SDI will be highly dynamic and pervasive environments of logical resources capable of executing any network and service function (e.g., from L2 to L7) developed and controlled as software applications. It is argued that SDI will be a first concrete impact of the Softwarization trend which is starting to impact (with different expressions, e.g., SDN, NFV, Cloud and Network Computing) the Telecommunications and ICT ecosystems.In this respect, the paper proposes the model of the Universal Operating System (UOS) for SDIs as an overarching and distributed Operating System spanning from terminals through the network elements, to the Cloud/IT resources. Then UOS functional architectures and some key challenges related to its development are briefly examined.Eventually, it is argued that this evolution towards SDI will definitely blur, on one side the border between the Telecommunications networks and the Cloud Computing, and, on the other side, the distinction between the Telecommunications networks and the future "terminals" connected to them (e.g., handsets, tablets, machines, smart things, drones, robot). This transformation will have profound techno-economic implications for the Telecommunications and ICT ecosystems