It seems simple enough but I must be missing something. As per the Help File I even verified that the "Non-Prime Public Network Identity" was set to "Yes." I set the directory number field to the extension that I want to change, selected CPN Substitution and then set the Associated Number field to the number that I want to appear, tried using a four digit and ten digit number. However when I place the call from the extension, the DID still appears on the caller ID.