billstewart writes "Network World has an article on networks of pneumatic tubes, which are still around in some cities, and also used in places like hospitals. As the article says, "Try delivering bottles of pills over Ethernet." There have been a number of proposals to take unused city pneumatic networks and run fiber optic telecom lines through them. Unfortunately, according to the article, most of them haven't actually worked out — 9/11/2001 interfered with the plans to do that around Wall Street, and city governments haven't always been cooperative, especially when their water&sewer departments want to run fiber through their own tubes. One company has some patents on doing it — the business model may be obvious, but getting the fiber actually blown through the tubes without damaging it apparently has some non-obvious techniques to it."