I set up a group-page with a four digit extension that is in the 6000s. Even though I have no other extensions in this range we still get misdials from outside callers and it activates the group-page speakerphones. Is there any way for me to block outside callers from dialing this extension? I have tried to fool around with the COR but I would need step by step instructions if that is the solution. Any suggestions would be appreciated.