If you want to make sure the queue always routes to a 3 way call, the instructions below will show you how to do that.
From the Dashboard, click on Call Center and select Call Center Queues from the drop down.
In Show Queues Section, click on the Action Button of the Queue, and select Settings from the drop down.
Go to the Call Routing Tab.
Scroll Down to Automatic 3way Calling. Select the Country and Type in the Phone number.
Click on Apply Changes.