Lucent Technologies Octel Unified Messenger Concepts and Planning Guide 101-1620-005 - Manual (Page 63)

Designing addressing schemes
101-1620-005 4-3
Local mailbox numbers
Local mailbox numbers are used to address any Octel Unified Messenger
subscriber in a voice mail domain from the telephone user interface.
Traditional voice mail systems typically use this form of addressing.
Within a voice mail domain, all local mailbox numbers must have the
same number of digits. Each local mailbox number must be unique within
the domain. Many organizations use telephone extension numbers as local
mailbox numbers. This means that a separate directory item for mailbox
numbers does not need to be maintained.
In a Centrex environment, many organizations use only the last four or
five digits of the subscriber telephone numbers as local mailbox numbers.
This provides a shorter number that is easy to enter, but still unique. Other
schemes are also possible.
Note: A local mailbox number has no significance outside the voice
mail domain. For example, it cannot be used as an element of
an OctelNet address.