AT&T Classic Mail Voice Messaging System - Manual (Page 46)

In addition, some pagers may require a pause to allow
them to answer the page and display the number (or
mailbox) you should call, or an extra code such as the star
or the pound key. If a pause or a special code is required,
you embed them in the sequence of numbers by first
entering the star key. For example, if your pager requires
a pause, you would enter the pager number to call, then
the star followed by a number (1 to 9) to indicate how long
a pause (in seconds) is required, then your mailbox
number:
Pause 8 seconds
1 408 555 1212 *8 12
Mailbox Number
If your pager required a pound sign to be entered after the
number of the phone (or, in this case, the mailbox) from
which the page came, you would enter a star and pound
sign at the end:
1 408 555 1212 *812 *#
Pound Sign
CLASSIC MAIL System Mailbox User Guide