Slightly Off Topic....DNIS Numbers

I think I understand the reasoning behind 8XX DNIS numbers. However, here’s what I don’t understand…

Let’s say we have the following:

800-800-6542 it’s DNIS digits are 6001

I understand that the system “see” the 8XX call coming in. It knows the DNIS digits are 6001. It routes that call to the appropriate number. However, why 6001? Why can’t the last four digits of the 8XX number be used?

Ours does not match the last 4 digits of the 800 number but 4 digits they provide to use do match the line that the 800 is tied to. So if you dialed that local number you’d get the same IVR recording as dialing the 800#. Maybe it’s the same for your setup?