Build route 001 to use Pool A which has the PRI/ T-1 channels in it. Then set up Route 002 to use Pool B which has your local LS/DS lines in it.
Go under Services to SCHED: NIGHT, press Show, set service to manual. Press Next and set OVERFLOW to Y.
Under DEST CODE 9 set NORMAL: 002, press Next and set NIGHT: 001.
Then whoever is the control set will press Feature 873, Password is 266344. The screen will show SERVICES ON. This will stay on the phone at all times. If it doesnÆt then your overflow is no longer working and all calls are going out over the local lines.