Thus, the “black box” was invented. Black boxes were devices that, if I remember correctly, kept the voltage on your phone line from dropping. Apparently when your phone rings it is at one voltage, but when you pick it up the voltage drops. This is how the phone company (at least used to) was able to detect that you had answered the phone (which was also when billing began). Since the black box kept the voltage from dropping, the phone company could not detect that you answered the call, and billing was never started. Phree calls!

By the time I began reading about black boxes (the early 80’s) they were already being referred to as “something that *used* to work.” The story I heard back then was that they were often used by bookies so that people could place toll free bets.

Apparently black boxes officially quit working when digital switching was introduced, although I suspect the phone company caught on long before that (”Why are people letting a phone number ring for an hour?”). You are right, when everything goes 100% digital all these old tricks and techniques will quit working, or at least move aside for all new tricks and techniques.