How it works
A PBX maps extensions to users, softphones, ring groups or call-handling rules. An extension is not necessarily reachable directly from the public telephone network. A consistent numbering plan helps avoid conflicts between teams and locations.
Business example
Employees dial extension 203 to reach accounting without needing a separate public phone number.
What to consider
Check numbering uniqueness, call-transfer rules and how extensions behave across offices. Renumbering can affect IVR menus, forwarding and internal directories.