Short answer, I would go under trunks/digital trunks and find a working T1 trunk. There is should show you the Trunk service assignment value, find this in trunk attributes and see what is absorbed/andor added and whether did table is being used.
This will help as the value may be in the did table under call handling/call routing at the bottom or it may match extension direct or be a system speed call. sytem speed call is under system whatever the second section.
I know there are others out there that could provide the full path, but I don't have anything open and usually don't read the headings any more