Network virtualization realizes the vision of an Internet where resources offered by different stakeholders are used and shared by multiple coexisting virtual networks. The abstraction introduced by network virtualization opens new business opportunities. The authors expect that in the near future, infrastructure providers (or resource brokers and resellers) will offer flexibly specifiable and on-demand virtual networks over the Internet, similarly to the elastic resources in today's clouds. This paper initiates the discussion on the optimal resource allocations in such an economic environment. They attend to a scenario where a flexible service (such as a web service or an SAP database) is implemented over a virtual network. This service can be seamlessly migrated closer to the current locations of the (mobile) users.