I have been using Oracle VirtualBox for a couple years, but since we're upgrading our server OS from Windows Server 2003, now I like to switch to Microsoft hyper-v environment. I was reading through licensing.
To run Windows Server 2003 guest under Windows Server 2008/2012 hyper-v role, I need CALs for both, guest and host.
To run Windows Server 2003 guest under Hyper-V server, I need only CALs for Windows Server 2003.
I talked to 3 Microsoft Licensing specialists, two of them says, as long as I use the host as only management for hyper-v, I don't need to purchase new CALs for host OS. One says, I need to purchase the equal amount of CALs as the guest needs.
I have to purchase CALs for 2012 when I start moving clients to new server, anyway. But it seems as Microsoft wants a good payment at one shot.