Existing switch markings for telephone numbers are mechanically manipulated via the Recent Change channel to provide an appropriate treatment. In case a call to a vacant pooled-in number cannot be completed, a terminating switch, instead of generating a REL message with a Cause Code 26 and tearing down the call, connects the call to an Operations Support System that provides a predetermined announcement to a calling party. Calls directed toward numbers that are ported-out are placed on a Machine Intercept, which results in sending a cause code 26 to an originating switch.