Wire up all in parallel as shown... There are 3 legs on a pot so use the middle
one and one of the outside ones. Find out the positive line of the phone with
a multimeter. Connect the stripe end (|| end) of the diode to the positive line.Connect the other end of the box to one wire in the phone, with the other wire
going to the socket as usual.
Pick up the phone. If you do not hear the dial tone, turn the pot until you do.
If you did hear the tone, carry on from here (even if you did above). Turn the
pot down until the line goes dead. The box is now ready. If someone calls you,
pick up the phone and you shouldn't get charged.
I've been told this works on System X exchanges, but only for 6 minutes, then
you get a message. I had difficulty as I had a wide adjust pot that took 25