By using the excess capacity of foreign telecommunications firms, callback companies can offer overseas calls in Hong Kong.

CNN: Getting Ready for 1997

The APIs can work in both directions, serving the content and triggering callback functions to report on user activity.

FORBES: For Real Content Monetization We Need Industry Standard, Two-Way APIs, And Fast

In yet another wonderful callback, UNIT troops appear to help Shard employees who are returning to their former, uncontrolled selves.

FORBES: 'Doctor Who' Review: 'Bells of St. John' Is a World Wide Web of Intrigue

And I don't want to deprive the 6.2 million citizens of Hong Kong of the choice to use IDD or callback.

CNN: Getting Ready for 1997

In a recent job search workshop I led, a talented, well-educated and experienced professional listed a number of callback interviews that went nowhere.

FORBES: If You're So Good, Why Hasn't Anybody Hired You?

To our mind, callback is really an encroachment on our license.

CNN: Getting Ready for 1997

It also felt like a callback to a solid bit from Season 1, in which a water bottle tumbling from a high window crushed a different car.

NEWYORKER: Black and Blue

But the best callback of all is to Clara.

FORBES: 'Doctor Who' Review: 'Bells of St. John' Is a World Wide Web of Intrigue

They are then reallocated to the party they voted for at the last election on the basis of values derived from a 5, 000 sample callback poll immediately after the last election, when Populus re-interviewed people polled in the run up to the election.

BBC: How poll tracker works

What about callback services?

CNN: Getting Ready for 1997