Be nice to have that manufacturer/controller/model info. I like to use the Viking C-2000 or C-3000 with the K-1700 Speakerphone (among other combinations). Those have programmable disconnect timers, so nothing needs to be done on the PBX side.

If you disable those timers, the door "won't turn off" until you remove power from the controller or door strike circuit.

"Press play and record at the same time" -- Tim Alberstein