PBXs are usually not used for the main routing of phone calls, but rather for the introduction of a call into the larger network and for the routing of a call from the larger network to its final phone. If you know what PBX stands for you are a Telecomtechie. The Mack Daddy phone switch is the 5E . They are switches which serve as the gateways to the phone networks of entire nations. If one of those went down, so would most of the communications along the northeast Atlantic coast of the United States.
Switches send information through the network, oftentimes through trunk lines .
Formerly copper, most trunk lines are now fiberoptic cable. This should not be confused for a proposition from an elephant. You ought to be able to disguise yourself in the industry pretty well too. This Project Galactic Guide site owned by Alex McLintock .