Altigen ACM 6.7 Administrator's Manual page 63

Figure 10. System Configuration, Number Plan tab
Use the Number Plan tab to specify the following parameters:
Parameter
Extension
Number Length
Default Password
Description
The number of digits for your extension numbering system. Valid
entries are from 3–6. For example, extension 2001 and 4020 are
4-digit extension numbers.
Note:
Once the first extension is configured, the extension number
length cannot be changed without totally reconfiguring the
system or deleting all the extensions already configured.
Further, if a first digit dialed is assigned to extensions and
you have set up extensions beginning with that digit, you
cannot change the digit assignment without first deleting all
affected extensions. For example, if 7 is assigned to
Extension and you're using extensions 7010, 7113, and so
on, you cannot reassign 7 to IP trunk access, without first
deleting all the 7nnn extensions.
The default password for newly created extensions is randomly
generated by the system. (When the password is changed, it must
be four to eight digits in length.)
Setting a System Number Plan
MAXCS ACM 6.7 Administration Manual 49