callback

palautuspyyntö The return of a situation to a previous position or state.
puhekieltä A return telephone or radio call; especially one made automatically to authenticate a logon to a computer network.
2007, James M. Lepkowski, Clyde Tucker, J. Michael Brick, Advances in Telephone Survey Methodology (page 318)

For example, multiple callbacks might be made to a nonanswered number to increase the response rate.