Windows Small Business Server 2003 and 2008 (SBS2003 and SBS2008) are still widely in use, but CALs for these are no longer available for purchase. So, what if you require more CALs but cannot get rid of your old SBS?

SBS 2008 and SBS 2011 work on a trust-based CAL count, so they do not need activation. You can simply purchase SBS 2011 Standard CALs and exercise your downgrade rights. Note that this cannot be done with SBS 2011 Premium CALs as they contain features that are not the same as in SBS2008 Premium.

Unfortunately, for SBS 2003, it's not that simple, as it uses online activation for CALs. In this case, you still have to buy SBS 2011 CALs, which are legally usable on your SBS 2003,  ...