How do long distance calls actually work?

When calling a friend thousands of miles away, there is a lot going on between your mouth and their ear. It is pretty amazing to think that 150 years ago it would have taken weeks to get correspondence from California to New York and now it can happen almost instantaneously. Let's consider what happens in those microseconds it takes to get the sound of your voice to your friends phone receiver.
There is a lot of computer technology that has gone into making your call happen. A historical overview of how modern phone systems have evolved over the past few decades will help us to understand how they currently function.
At one point, long distance calls were routed through a very simple system by a human being sitting in a town's central office normally located in the middle of town. From here a set of copper wires was run to every phone, connecting to each individual's telephone receiver.







