Messaging provides the ability to centralize the system using full E.164 mailbox numbers, yet each site has the ability to have short mailbox numbers.
You can configure mailbox numbers using less than the full E.164 number and map these mailbox numbers to a full E.164 number. Thus, users at any site can continue to use mailbox numbers locally that are smaller in length, but are still uniquely identifiable in the global context.
Messaging supports only those mailbox numbers that have a fixed length system-wide. Messaging does not support those mailbox numbers that have a variable length.