Network function virtualization and software-defined networking have the potential to change provider revenue streams and offer new services. We measure the impact of NFV on large provider networks by accurately modeling a contemporary service provider. In our model, we consider actual equipment that is currently deployed and understand the impact of NFV on CapEx, OpEx, and service delivery. Apart from accurately modeling a contemporary provider network, we also inculcate robustness in the model to factor in for uncertainty of network traffic. We answer the key questions: what functions in a network can be virtualized and which functions need to continue as traditional hardware? We also harp upon the question as to what new services can be considered and in which circumstances? Our model considers various combinations of network architectures that are used in contemporary networks. The model is supported by extensive analysis and simulation that verify our results from cost, performance, and scalability (of services and the model itself) perspectives.