Numbers Stations: "five-nine-three-four...."

As a child (this was before the Internet!), listening to shortwave radio was a fascinating way to connect to the outside world. One of the intriguing features of this world has long been the so-called numbers stations - usually automated voices simply reading out streams of digits all day long. BBC4 has just broadcast a nice documentary (RealAudio stream) on these stations. Radio Sonder Grense has also had a documentary about such stations in Afrikaans. As usual the Wikipedia entry Numbers Station has a lot of additional information and many links.