Not much more to say. At one point it was much cheaper to proxy media to Canada and back into the US than it was to route it straight state to state.
It has to do with treaties and international tariffs versus state to state. When you hit a certain scale, say Verizon scale, you get to have your traffic carried for free by the other major telcos. It's all a volume game.
In short, people without volume maximize the rules of the system in order to increase their margins. One such method was to pretend calls were coming in from Canada when they were actually state to state.
Another odd fact: Calls Intra-state (from one county to another) are just about universally more expensive than calls Inter-state. The reason is, when you call out of the state, more often than not, someone is paying for receiving that call, but when you call intra-state all of the cost is born by the local operator.
