This is straight from the manual...
Hiding User Names in Voice Mail Directories
You can hide programmed descriptions in the Voice Mail Directory. For example, a user may
have a primary extension at the office programmed as “Bond, James.” However, the same user
may have a secondary extension—for example, at home—that is not published from the Voice
Mail Directory.
Because the IC directory is intended for internal use, both primary and secondary extension
entries appear in the IC directory. There may be any number of primary (no tilde in description)
and secondary extensions (first character of description is a tilde). To differentiate between
these two, an asterisk appears immediately before the secondary extension entry—for example,
“*James Bond”.
To hide an entry in the Voice Mail directory:
Enter a tilde (~) in the Description field immediately before the last name—for example,
“~BOND, JAMES”. The tilde character (~) makes the entry inaccessible in the Voice Mail
directory. Note that if someone knew the number of the secondary extension, they could
dial that extension directly. Someone entering “BOND” (2 6 6 3) at the Voice Mail
prompt, however, would find only the primary extension.