I just wanted to pop in and clarify that frozen users are not deleted; those accounts remain in the system indefinitely, although usernames and pet names become available to use after a certain period of time. There is sometimes some confusion over whether self-freezing an account deletes it, and the answer to that one is a big "no!"

As far as taking pet names or usernames of inactive and frozen accounts, Desolace is correct -- you'll have to wait until it is officially "cleared," at which point you can simply use the name without any intervention needed from staff members. :)