Hello, Hello? HELLO!, Yes i'm here! Wait, I can hear you.... Hello! CLICK! Dial Tone.....
The joke requires the temporary modification of the telephone handset. The joke works with virtually any telephone that has a phone base and a separate handset that are connected together by a modular (snap in) connector. Handsets with pushbuttons on them will not work, nor will telephones that have the handset and base 'hardwired' with no modular connector.
All you need is:
1. 'victims' telephone
2. Some transparent tape
Step 1: Locate the Modular Connector on the Handset and disconnect it.
Locate the connector on the bottom of the handset (part you hold to your head) and disconnect the cord. This is done by finding the tab sticking out of the connector and pressing it toward the cord while gently pulling the connector away from the handset. It should easily slide out of the hole in the handset. Do not force it.
Step 2: Tape over selected contacts on the connector
Taping over the contact is easily done by pulling out about an inch of transparent tape from the tape dispenser, but leave the tape hanging on the dispenser. Take scissors and and cut down the length of the exposed tape to produce a thin strip just wide enough to cover the selected contact. Tear the tape off of the dispenser and position it over the desired contact on the handset connector. Press it in place and trim off any potion of the tape that extends past the connector body.
Note, that anecdotally it appears that the wiring convention shown may not always be followed, so it is always best to test the set up before putting this in the hands of the victim.
Step 3: Insert Connector (with tape) back into the handset and test.
Test your work by calling an accomplice to see if you cannot hear them, but they can hear you (or vice versa if that is the arrangement that you want.) If it does not work try rearranging the tape location.
Enjoy having your 'victim' get frustrated with the phone system that just does not work!
To 'undo' the joke, just remove the connector and remove the tape and replace the connector into the handset!