Virtualization at the processor layer is such a poor interface to indicate what your apps want to do. There is already so much virtualization in the standard kernel, it just needs to be extended a bit and OpenVZ has done just that. No more disk images for your guests, it’s just a directory tree. Provisioning is a snap. You only get Linux though, but you can use KVM (and XEN xen — eww) if you need to share the hardware with a different OS also.

I wouldn’t touch Vmware, XEN or KVM for a VoIP media workload, but I would with OpenVZ under the right circumstances.

Mike