Tie one of the black cords to the black telephone's handset. You need to tie it very tightly so it doesn't come undone even if you tug at it.
Hold the handset, keeping it at a distance from your face, and dial 20406080; after that put the handset back in its resting position. Then lift the handset again and dial 25515823. Leave the handset lying there, whether the line gets connected or not. (Even if it does get connected don't answer it.)
Keeping noise to the minimum, creep into the nearest room from where the black telephone is, and close the door behind you. Wait for one minute.
Get out of the room and go back to the black telephone, lift the handset and repeat the procedure 2.
Keeping noise to the minimum, go into the second nearest room from the black telephone and wait for one minute.
Get out of the room, put the handset back, and repeat the procedure 2
Keeping noise to the minimum, go into the third nearest room from the black telephone, and wait for one minute.
Get out of the room, put the handset back, and in this state dial 22822.
Enter the fourth nearest room from the black telephone with your eyes shut. As soon as you're inside, tie the second black cord to the doorknob in a double "8" shaped knot.
Open your eyes. Don't utter a word no matter what happens.
Draw back the curtains and if the windows have all turned black (it means you are in another world**).