I had an old phone lying around, so I decided to do something cool with it. This is what I came up with. The "headphone phone" is an old phone converted into a headphone.
Step 1: Things You'll Need
1. Old telephone.
2. Phone cable.
3. Headphone jack.
4. Phone plug.
I got most of the parts from a phone, but I'm sure RadioShack or someplace has them.
1. Soldering iron.
3. Electrical tape.
4. Wire strippers.
5. Alligator clips
Step 2: Making It
Strip the wires on the headphone jack. Strip the wires on the phone plug and connect them to the Jack using the alligator clips. On my phone plug, it was the green and red wires, but you might have to experiment (if you still cant get it to work; go to step 2). After you figure out which wires to use solder them together, wrap the electrical tape around one side so the wires don't touch, then wrap it around both.
Step 3: Upgrades
If you have trouble or just can't hear it at all, try turning the volume up high, or you can make the amplifier from the link below. If it still doesn't work, then you may have to take the phone apart and make sure you are connected to the right wires.
Another upgrade could be switching out the speaker on the phone with a different speaker. You could really just cut the end off the phone cable and solder it directly to the jack, but I chose not to.
If you have any questions, feel free to ask!