I heard this somewhere, and I don’t know if it’s true, or just a phreaker’s urban legend of sorts – an old, old crank telephone from the late 1800s, one without a dial, can still be connected to a modern telephone line in the United States and recieve calls just fine. If the phone is cranked, you’ll reach the operator.
Is the telephone system thatp backwards-compatible?
The phone will work as a receiver, but if you try cranking it, you might get a nasty call from the phone company (this may not be the kind of operator contact you had in mind) and possibly a fine. The crank is a small AC generator that puts ~90 volts on the line. The phone company has its own generators and would defintely frown on someone injecting his own 90.
Hand-cranked telephones are still in use in the military (though being replaced by ones with batteries) and will remain a CIA interrogation standby for years to come. The standard TA-43 field telephone (gradually phased out over the last decade) has a hand-cranked generator designed to activate the ringer at the other end, but only needs 2 D-cells to transmit a normal conversation.
Telephones are actually pretty simple devices, not greatly changed since Alexander Bell walked into the patent office. The most likely reason an old phone wouldn’t work is if the line has been set to carry digital signals, which is becoming common in office buildings with local exchanges. As long as your phone line is “analog”, you’d have to go back pretty damn far to find an incompatable phone.