A group of users can be created with a purpose of receiving voice announcements through the speaker of a telephone set, but it has to be in the waiting mode.
In telecommunications the automatic call-back is a computer telephone function which allows the user by the engaged addressee’s line or in the other case of the subscriber’s inaccessibility indicating the system to save the number of the called subscriber and make the call when the line will be available or when the called number is not engaged.