I need to check on and add a phone number to a Cisco Router

We have acquired a new office that has CISCO UNITY EXPRESS for thier phone system. I have learned the basics of it and can now assign phone numbers to extensions within the system. I just had a user complain to me that her outside line or "DID" was "OUT OF SERVICE" she went on to say she did not even know she had an outside line until a few days ago and after she started giving the number out she realized it did not work. I check the Unity and everything looks ok. The Mac of her phone is assigned to her internal extension. She can and has always made out going calls from this phone. The phone number is within the range of the rest of our DIDs assigned to this office. I called our provider and was told there was nothing wrong on their end. The number just not appear to be in our system. I logged into the Unity and swapped our her phone number with a number that I know is working and her phone started receiving external calls from the new number and the phone I gave the non working number to started reporting "OUT OF SERVICE". I have been asked to "Look at the config file in the router and confirm that number is set up the same way the rest of the DID numbers are from the CLI". I know a few Cisco basics and can log into the router, but not sure how to research if the number in question is actually entered in the Cisco Router. I need some basic SHOW commands that would let me display this number and if or how it is set up in the rounter and if so how to add it to the router. All advice on basic Cisco Voice is welcome