Most of the time they will just give you the activation key if you call and ask with the CD key that you have. The only time they wont is when you give them a CD key that has been flagged as pirated. So if its someone's CD key from their home computer that is legal, they wouldnt know and would just hand over the activation. Its mainly for them to prevent pirates fom distributing the software from one CD key and making $ from it that doesnt go to them. f its between friends then its harder for them to track if its your own CD key or a friends.

Most sofware protection can easily be circumvented with a little brains or a little work.