[LARMGUY]

the phone has dc on it. an ac signal is sent to ring it. the ac and dc are on the same 2 wires. think of waves on the ocean. waves on top of the tide. some times it adds, sometimes it subtracts. in this case it is additive. put a voltmeter on your phone and watch when you ring it.

Better yet, wet your fingers and put them on the 66 block when someone rings in. Pow!