PURPOSE: To obtain a main wire outgoings from extension subscribers which can obtain the main wire outgoing only through the operator, by temporarily changing the class when the operator is absent.

CONSTITUTION: An extension subscriber A which can obtain the main wire outgoing only through the operator because a main wire outgoing regulation class is set, calls the operator at a B board ATT through a connecting pass 1 to obtain a main wire outgoing. When the operator does not answer within a specified time, central control unit CC detects this and temporarily releases the main wire outgoing regulation class of the extension subscriber A, and then, connects the extenstion subscirber A with an outgoing register OR with a connecting pass 2. After listening the dial tone from the OR, the extension subscriber A can obtain the main wire outgoing through the connecting pass 1 by operating the dial for the main wire outgoing.