If you’ve installed Office Communication Server 2007 on a machine running Windows Server 2003 x64, you will probably not see the Communications tab in Active Directory Users & Computers or dsa.msc. You also find the Communications server options missing when you right click on the user account.
This is because you are opening the 64-bit MMC snap-in for Active Directory Users & Computers (which is default) instead of the 32-bit MMC snap-in.
To open the 32-bit MMC snap for ADUC, go to Start –> Run and type
The Communications tab should now be available and you can right-click on the users to get the Enable users for Communications Server option and more.