One of the goals of Prism was to avoid coupling too closely with any particular Dependency Injection container. To that end, the first version of Prism had defined an IContainerFacade that anything from the library side of Prism would interact with and we supplied an adapter for Unity Prism.
It turns out there were a number of people interested in a common definition of a service locator interface that applications, frameworks or libraries could use for a similar purpose. Adapters to specific technologies could then be written once and re-used. To that end, the CommonServiceLocator project was established and a number of folks in the .Net community worked with patterns & practices to help define what this interface would look like.
For Prism, we removed our IContainerFacade interface and started using the IServiceLocator interface offered by this project. As Prism V2 is focusing on both WPF and Silverlight, we had ported this interface to a Silverlight version and we have now posted the Common Service Locator for Silverlight binaries to Codeplex.
Hopefully you will find these useful.