How to build a 3-way phone

Step By Step:

   1] You will need two different lines for this.  Okay first take
      off both of the boxes covering the wires

   2] Take the green and red from each box and attach a wire to
      each of these one wire to green 1 wire to red same on the other
      box

   3] After you have 4 wires (2 For each box) then get a two way
      switch with two terminals then hook the two green wires to
      one side and the red wire to the other side then when you
      switch the switch you should here a dial tone and then just
      dial out and you will be able to talk to two people at one
      time

[ Note from Tommy: When I was much younger and stupider I tried something
  like this... it worked for about 10 seconds at a time then the audio
  returned from the two far ends of the 3-way started to cancel each other
  out s l o w l y by phase inversion and conversation became impossible...
  if you're going to try this at least put a pre-fabricated FCC Part 68
  interface on each physical line you connect... at least then your own
  incompetence won't draw unwanted attention from your local service
  provider, who I can assure you has significant clout with your local
  police... hint hint, take or leave as you wish... ]