An audible difference if hard to accomplish, but a VISUAL difference is easy... sent the calls to different call routing announcements named "COMPANY A", "COMPANY B", and "COMPANY C" then remove the greetings and have them timeout to the appropriate answer destinations, then when the phone rings the display will show "Xfer From COMPANY A" so that you know which line/DID is ringing in. Might be a simplier to retrain the people (hehehe, yeah, I know) then try to find a oddball solution.