Before modern electronic telephone switching systems came into use, dial tones were usually generated by electromechanical devices such as motor-generators or vibrators. In the United States, the standard "city" dial tone was a 600 Hz tone that was amplitude-modulated at 120 Hz.

How does tone dialing work?

Tone dialing, also called as Dual Tone Multi Frequency, uses different tones to indicate a different number. Instead of sending multiple signals for each digit, it would only need to send one for each. ... Tone dialing handsets use a numeric keypad where you simply push each digit.

Where did the calling sound come from?

Several countries used dial tones before automatic switching came to Norfolk. A German historian named Dietrich Arbenz traced the invention of the sound to an engineer named August Kruckow, who helped set one up in Hildesheim in 1908.