If you are managing a server, be it
SCOM, SCVMM etc, it will need one of the SC2012 packs, be it Datacenter or other. From what I can see, virtual server hosts will probably want DC, and normal servers, the standard.
I 'think', from my conversations, that the packs cover installing management servers AND all SQL technology, reasonably needed for that purpose.
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CAL's for the 'normal' clients are covered in the Enterprise CAL pack at the moment.
This may change when 2012 actually is released, but I can't see it being much different, you pay for the Enterprise CAL pack, you get Enterprise CALs!
All licensing at the moment covers the 2007-2010 versions of SC, as SC2012 is only RC at the moment.
Thanks
James