I recently discovered that the radio show L'etranger, on Radio Panik, 105.4 in Brussels, used shortwave radio recordings of pirate radio and numbers stations, from the SWLing Post and other sources, in one of their mixes of eclectic music and sound clips. The end result is a splendid piece of sonic art.
Note that their audio is only available on archive.org until May 23, 2013. Click here to download the show, or listen via the embedded player below. You can also hear the show on the L'etranger website.