The way it works is that for a Direct Call to CUC (like pressing the VM button on a phone), CUC looks at the calling number and uses that to try to match a voicemail box in order to send the call to the Sign-In Conversation.
If you need to change the "dialed number" that CUC sees (because the extension on the phone does not match the extension on the VM Box) you can mask the number using the Voicemail Profile. CUC will replace (or mask) the calling party and try to match on the changed number.
So, if your user has an extension of 8050 and their VM Box also has an extension of 8050 then you don't need a mask on the VM Profile because no change needs to be made.
Most of the time, users' extensions and their VM Boxes have the same number. So most of the time a single VM Profile with no mask can be used for all of your users.
I hope this explanation helps. Let us know if you have additional questions.
Maren
