资料来源 : Free On-Line Dictionary of Computing

cost control callback
     
         A system where a computer automatically
        rejects incoming {dial-up} calls from certain telephone
        numbers and calls them back, with the result that the caller
        pays nothing for the connection.  This differs from security
        {callback} in that it applies to certain phone numbers instead
        of to certain user names.
     
        (2003-07-13)