AT&T MERLIN LEGEND Release 4.0 Feature Reference page 546

Feature Reference
use those digits as the leading digits for a longer extension number. For
example, if extension numbers 1, 2, 30, and 40 are assigned to
telephones, those numbers cannot be used as the first number in longer
extension numbers such as 10, 200, 302, or 4052.
Whenever an extension number is renumbered, the original extension
number is available for use.
The reserved system-assigned extension numbers (shown in Figures 41,
42, and 43) must be assigned a new extension number before the
original extension number can be used for anything else.
The system offers three numbering plans:
2-Digit
3-Digit
Set Up Space
Each of the plans allows renumbering of all or selected extensions (single or
block). The system numbering plans, with the numbers they automatically
assign, are shown in Figures 41 through 43 and are described in the following
three sections.
NOTE:
Figures 41 through 43 show the default settings in the gray spaces. Extensions
can be renumbered to any number shown in the white spaces.
2-Digit Numbering Plan
The 2-digit numbering plan is the factory setting. This plan is designed for
companies with fewer than 50 extensions that do not anticipate a need for more
than 50 extensions in the next one or two years.
Figure 41 shows the numbers automatically assigned by the system.
The numbers in Figure 41 are arranged in rows according to the first digit. The
type of equipment, jack, or feature to which they are assigned is indicated in
each block within the row.
546
System Renumbering