Schematic for box that makes a pair of payphones into a divertor for defeating
caller ID....  Designed by Vox Dei (ecorliss@efn.org) in March 1994.

                  _________________________________________________
                 |         _____________________________________                  |
                 \        /                                                                                      |                 |
                  \/\/\/\/                                                                                       |                 |
                 ==========  A                      ___/\  /\  /\  ____                  |                 |
                  /\/\/\/\                                        |         \/  \/  \/         |                 |                 |
                 /        \                                       |                            |                 |                 |
                 |         \________                   |          B                |                 |                 |
                 |_____________\_______|                             |                 |                 |
                         |    /           _______________________|                 |                 |
                         |    |           |    ____________________________ |                 |
                         |    |           |    |                                                                                    |
                         |    |           |    |            |                                                                       |
                      |///|   |> <|><|    |> <|><|                                                                       |
to in-  _____|             |                |                                                                             |
coming           C      D|             E |                                                                             |__
 line   ___________|                 |                        to outgoing line
                                                      |_________________________

A -- 1:1 transformer
B -- resistor
C -- coil of relay
D -- switch 1 of relay
E -- switch 2 of relay

It works like this:

While both phones are on-hook, the 50 volts on the incoming line is not
enough, with the resistor in place, to close the relay.  When someone calls
that line, the power will go up to 90 volts, and this should be enough to
close the relay.  When the relay closes, the incoming line will be switched
so that it goes through one side of the transformer and through the coil of
the relay, keeping the relay open, and the outgoing line will be switched
through the other side of the transformer.  Any AC on either side of the
transformer should show up on the other side...  When the person who called
disconnects, the phone system will drop the line voltage of the incoming
line to zero for about a second.  When this happens, the relay will open
again, disconnecting both lines, and the circuit will be ready to take the
next call.

Ummm....  Currently this design will only work for calling 1-800 numbers
and making collect calls, so I'm trying to figure out a way to be able to
use red box tones to make other types of calls...  The problem is that I
don't know how the coin test works on payphones -- according to the Book
of BIOC, a red boxer should insert at least a nickel into a pay phone so
that if the ACTS computer or an operator sends a coin test signal the
phone won't tell them that there are no coins in the collector....  Does
anyone know how this signal is sent and how a payphone responds to it?