The Times has an interesting story about the origins of the dial tone, and why telephone companies had to implement it before they were able to switch to automated switching networks. Before then, Bell System and ran its switchboards with a corps of "hello girls" that would manually connect callers to their requested lines. Just as it's difficult for a generation of cellphone users who may have never used a rotary telephone to grasp the concept or necessity of a dial tone, there was a generational of early telephone users who didn't know what to do when faced with that humming sound for the first time. Also fascinating: original dial tone sounds are difficult to reproduce electronically, even though their frequencies are documented in manuals. And of course I never want to miss an opportunity to remind you of this awesome 2012 story about the mechanics of the dial-up modem handshake. Update: reader John Carlton sent over some great links to short informational films that were created to introduce the dial tone to new users. I've embedded them below.