Actually, there is a germ of truth in this. On older phones (don't know if this works on newer electronic phones) when the handset is 'on-hook' a switch opens and breaks the voice circuit. This of course only works for DC circuits. If you drive that same circuit with an AC signal . . .
There's another angle I may have mentioned before. Many electronic phones come with a ``feature'' that allows you to call home, produce an electronic tone and eavesdrop on your own house. When the tone is sounded, the ringing stops (or never starts) and the phone goes into ``off hook'' mode (i.e., the microphone in the mouthpiece is turned on).
Even if you did not buy this feature when you bought your phone, it is still there, just waiting for that electronic tone. You can't produce it, because you didn't buy the doohickey, but anyone with such a doohickey can call your house and listen in. . .
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Devices of this type are known generically as "infinity transmitters." They will not function anywhere the phone network is run by a digital (4ESS or better) switch. In a modern switch, the ringing you hear is being generated by the switch, the switch is simultaneously ringing the number you dialed, however the two are not physically connected. The actual connection is not made untill the far end answers, this was implemented to stop various types of fraud, and unauthorized eavesdropping. Brian D Williams Cypherpatriot