This object reports the module number, as labeled by the operator, that this phone's port belongs to, assigned according to which expansion port on the Control unit the module is plugged into, with module number 0 reserved for the Control unit itself. Administrators use it together with the port number to fully locate a phone's physical connection on a multi-module IP Office system. For example, module number 2 identifies the expansion unit plugged into expansion port 2 on the Control unit, and a phone showing that module number is connected somewhere on that specific expansion unit.