isdn caller — interface
phone-number[callback] no isdn caller
ISDN caller ID screening
If your ISDN switch supports caller ID, this command lets you specify a
phone-number from which incoming connections are allowed. If the inbound call does not originate from this number, it will be rejected. You may use the letter
x in the phone number as a wildcard character; for example,
458-xxxx means “any number in the 458 exchange.” The
callback keyword causes the router to reject the call and initiate a callback to the caller’s number; this feature may help you manage phone costs.