It is a call which is made over internet protocol (VoIP). For example,
one can call using Google Voice to other recipient located miles away. Such
call can also be international.
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.