I said "probably" because I have seen this many time. In my many years of experience I have seen that casual administrators don't keep track of DIDs, unless a translation is created in IOS or CUCM incoming, and not even then, because they ignore what else are free. Big companies buy bulks of numbers, then don't use a lot, sometimes.
It is a common, real life problem, always asking "do we have any free DID" etc.
Also some users think their extension is their DID, and then identify their problem via the DID, and not the extension, especially now that many people work from home, use remote profiles, share lines, etc.
It just simply takes times just to identify who is using the EPNM as DID.
The original answer from Jaime Valencia (Cisco) is conceptual: like 'go study the system'. He may be right, but in the end, that is not a solution. In my view it is a shortcoming from the system, that I cannot for example list and search properties by line appearance in the web interface.
That being said, many installations use the EPNM to represent ANI to the trunk/gateway. But there is no simple way to check that. Of course, I am still to find the first small deployment using Calling Party Transformations into the Gateways... not a chance.
The misconception from Cisco comes from expecting only the best practice, maybe e164 and sip all across the board, and number globalization. The misconception is on the understanding of casual administrators, who cannot use this, don't understand it, are using old system with just a short extensions. And get frustrated sometimes with how difficult is to do the simplest things.
BTW, instead of criticizing a command, please propose a better command. For example: Instead of select *, select "1234567890" to find this line appearance pkid. Or better, propose a better inner join command with the other table to show this with the device and extension.
Extra solution to this problem: Export the lines or device in bulk administration and analyze the CSV.
Again, not simple.
