New network architectures are often promoted initially on the basis of cost savings, but then acquire more nuanced justifications as they near real deployments. Small cells, carrier WiFi and now virtualization: all major shifts which seemed to promise to slash operators’ capex budgets, but are now being adopted for a far wider range of reasons (often because the dramatic cost savings prove elusive in reality). The benefits of new architectures in terms of quality of experience and the ability to support new revenue-generating services often move to the heart of carrier thinking as deployment day approaches, and this was clear in discussions of virtualization and software-defined networking (SDN) at last week’s Mobile World Congress. Running network functions as virtual machines…