The Queues module is a more advanced version of the Ring Groups module. Like the Ring Groups module, the Queues module is used to create an extension number that your users can dial in order to ring multiple extensions at the same time. It also creates a destination to which you can send calls that will ring those multiple extensions.
However, you can program a Queue with some additional features. Individual extensions (called Dynamic Members) can be permitted to log into and log out of the Queue, so that when the phone is not occupied by a staff member who can answer calls, that phone will not ring. You can program the Queue to route each call to one open extension or all extensions, and use other ring strategies as well. A password can be required before a caller can enter a Queue. When a caller enters a queue, the system can play a music on hold recording instead of the usual ringing sound. Callers can hear expected wait times. They can be given the option to exit the Queue and have their call routed to another destination. Calls can time-out so that if the call is not answered in a certain amount of time, the call will go somewhere else.
For example, you could create a Queue that will allow your local phones to dial 600, and then the call will be routed to the next Queue member who becomes free. While the call is waiting, the caller can hear a special music on hold recording that is interrupted regularly with hold times, and with the option to press 5 to leave a message.
Because the Queues module creates a destination to which you can route calls, the Queues module is related to the any module that can route calls to a destination, including the Inbound Routes module, the IVR module, the Time Conditions module, etc. Because the Queues module is used to ring extensions, it is also related to the Extensions module. Because you can set an optional destination to send calls to if nobody picks up after a certain amount of time, the Queues module is also related to any module that can be used as a destination for a call.
See the User Guide