On some brands there is a direct correlation between the DID, but on 5000 you must establish that relationship yourself. A little more work, but much more flexibility (a given number could ring Joe this week, an announcement next week, and Fred after that). This relationship is established under SYSTEM/TRUNK RELATED INFORMATION/CALL ROUTING TABLES. Hopefully you'll find one or mare tables there with names like MAIN PRI or ATT DAY. Open up the most obvious one and you should see all your numbers with a RING IN TYPE (usually SINGLE) and RING IN DESTINATION for each. Just add your new destination extension where appropriate.
If you have to add your new PATTERN (the part of the DID carrier is sending) be sure it's not below the "+" pattern, if that exists. Plus means (any other number", and is typically used to catch DIDs you haven't yet put in the table.
This whole business is so flexible that there are many more complicated routing tricks that might be in place (such as also routing by caller ID or using only an exceptions table for night). Let us know if you find something strange and we'll help figure it out
