[Corelatus] said recently that “someone” asked them to identify the phone signals in the 1982 film The Wall, based on the Pink Floyd song of the same name. We suspect that, like us, that someone might have been more just the hacker part of the brain asserting itself. Regardless, the detective work is fascinating, and you can learn a lot of gory details about phone network in-band signaling from the post.

The analysis is a bit more difficult because of the year the film was made. At that time, different countries used slightly different tone signaling standards. So after generating a spectrogram, the job was to match the tones with known standards to see which one best fit the data.

The signal was not common DTMF, as you might have guessed. Instead, it was a standard known as SS5. In addition to the tones being correct, the audio clip seemed to obey the SS5 protocol. SS5 was the technology attacked by the infamous blue box back when hacking often meant phone phreaking.

The same phone call appears on the album, and others have analyzed it with some even deeper detective work. For example, the call was made in 1979 from a recording studio by [James Guthrie], who called his own phone in the UK, where his next-door neighbor had instructions to hang up on the operator repeatedly.

If you want to see and hear the entire clip (which has several phone-related audio bits in it), watch the video below. The sequence of SS5 tones occurs at 3:13.

Usually, when we hear tones in music, we think of Morse code. As for phone phreaking, we hear it’s moved to street kiosks.