The System Attendant can place CO/IP lines out-of service,

The System Attendant can place CO/IP lines out-of service, disabling outgoing calls on the CO/IP path. This is normally done should an undetected fault interrupt service on a CO/IP path. Incoming calls continue to be processed normally.
Operation System Attendant To disable/enable Outgoing CO/IP access (toggle)
1. Press the [PGM] button.
2. Dial ‘072’, the Attendant Station Program code.
3. Press the {CO} button of the line(s) to be disabled, confirmation tone is heard and the status for the selected line(s) is changed.
1. If the desired CO/IP line is in use, the System Attendant may still disable the CO/IP line. The feature will take effect after the desired CO/IP line goes to idle.
2. Once the line is disabled, all Attendant appearances for the disabled CO/IP line will flutter at 240 ipm, other stations will indicate the CO/IP line as busy, LED is On.
3. The CO/IP line outgoing access status is stored in battery-protected memory in case of a power failure.
4. Multiple CO/IP lines may be enabled/disabled without redialing the Attendant Station Program code. Confirmation tone is heard after each CO/IP line is enabled/disabled.
5. When the system detects a fault on an analog CO line, the CO line is disabled for outgoing access automatically.
6. Incoming calls on a disabled CO/IP line will continue to operate normally.