Last I checked it's called a "predictive" dialling campaign. Because having an agent listening to a ringtone is wasteful, it tries to guess when an agent will become free, and to have a just-picked-up call ready for when the agent becomes free. Sometimes it gets it wrong, and you end up answering the call to find there's no agent available.

Some systems are even devious enough to wait until you say "hello" before connecting you to the agent, and can tell the difference between a real person and an answerphone.

A "progressive" dialler is slightly less annoying, in that it'll dial only when an agent is free, but still saves the agent the bother of dialling themselves.