February 20, 2011 permalink
Bell Labs Dial with Music DTMF
From a 1950 issue of Popular Science, an ad featuring Bell Lab’s early multi-frequency signaling keyboard for connecting long distance phone calls, in the era just before DTMF dialtones were introduced to America’s households.
(Via the always-interesting History of Phone Phreaking blog, which links to a couple of other good vintage Bell Labs ads)