Internet Service Providers are becoming more in- volved in the audiovisual content delivery chain. One manifestation of this trend is the emergence of telco CDNs, i.e., content delivery networks operated by telecom service providers. In this work, we make the case for opening the telco CDN infrastructure to content providers by means of network function virtualization (NFV) and cloud technologies. We design and implement a CDN- as-a-Service architecture, where content providers can lease CDN resources on demand at regions where the ISP has presence. Using open northbound RESTful APIs, content providers can express performance requirements and demand specifications, which can be translated to an appropriate service placement on the underlying cloud substrate. To gain insight which can be applied to the design of such service placement mechanisms, we evaluate the capabilities of key enabling virtualization technolo- gies by extensive testbed experiments.