When I try to add mailbox 5050, Unity replies with "Extension 5050 is already in use by Ken Goldberg. Please enter a unique extension." Yet, there is no mailbox 5050 in Unity and if I try to add it by importing it from Exchange, it's not there. Any suggestions?
CallManager and Unity do not "share" extension information. They simply pass the DIDs back and forth for routing. If you deleted 5050 in CCM, it will not be removed in Unity.
In Ken GoldBerg subscriber profile, my guess is that his primary extenstion was 5050, then was changed to 7050. You added 5050 into the Alternate Extension field so anyone calling 5050, still got Ken's voicemail. Now, Ken wants 5050 as his primary again, so on the first page, you enter 5050, and hit save, Unity pops up the message saying it is already used.
Did you check in his subscriber profile under Alternate Extension (left column, down a bit) that 5050 was not in there?