This summer, with the advent of Pokemon Go (yes I am that kind of nerd), I learned that these phone booths were part of the Verizon Training Center. According to the Pokestop description, it's where linesmen learn their craft.
Aha, that's why there are so many telephone poles that seemingly go nowhere!
Around the back of the training building, you can see a dummy house to practice wiring to.
There are short poles to practice on the ground before moving up to the tall ones.
And once I even got to see training on one of the tall poles.
So cool to learn about the Verizon Training Center from a Pokestop and explore it! (Okay, so maybe this is one of those "dangerous" areas that the game warns not to enter, but I hardly ever see workers outside and stayed clear of the cherry picker!).