You can administer your system to call users back if users try to place an outgoing call over a trunk group when all trunks are busy. Ringback Queuing places outgoing calls in an ordered queue (first-in, first-out) when all trunks are busy. The system automatically places the callback call to the telephone when a trunk becomes available, and the user hears a distinctive three-burst signal, which indicates an Automatic Callback call from the system. When the user answers the callback call, the original call automatically continues. Redialing is not required. Ringback queuing is also called Automatic Callback for busy trunks.

If a user with a multiappearance telephone has an idle Automatic Callback button and tries to access an all-trunks-busy trunk group, the call queues automatically. The lamp that is associated with the Automatic Callback button lights, and the user hears a confirmation tone.

Ringback Queuing is automatic for a single-line telephone. After dialing is complete, the user hears a confirmation tone if the queue is available. No action is required. The system queues calls based on the value in the Queue Length field on the Trunk Group screen. The system checks the busy or idle status of the trunk group only once. If all trunks are busy, the call queues, even if a trunk has become available by the time that the caller finishes dialing. In this case, a caller might be called back immediately after the caller receives a confirmation tone and hangs up.

You can specify queuing for any outgoing-only trunk group that is not part of a distributed communications system (DCS), or for the outward direction of a non-DCS two-way trunk group.