Routing rules for unassigned numbers

I'm running into the same situation. I wanted to set up a "Catch-All" routing rule that would route any unassigned numbers matching our area code to our auto-attendant. I then learned that any outbound calls to our area code were being directed to our AA. I opened a case with Microsoft and they're saying this is by-design. They say that technically, external numbers are unassigned, so routing rules will match them. We need to be more specific with our Routing Rule matching configuration so that we're not matching external numbers. That would be easy if we had a block of numbers with no gaps, but numbers provided by Microsoft often have gaps between them. Microsoft is saying that the safest option is to create a rule for each specific unassigned number.