What this instructable allows you to do is change those headphones into a headphone socket, so that you can plug your expensive headphones in and enjoy movies/music on your phone like it should sound.
A photo of the supplied adapter for my O2 Trion XDA phone is below. It has some terrible looking headphones that I haven't even bothered to try out because I know they'll suck.
Step 1: What You Will Need
The second picture is a 2.5" to 3.5" headphone socket adaptor off ebay which cost about 99p ($2). NOTE that there is a wire inbetween them - don't get an all-in-one adaptor.
You also need:
Soldering Iron + Solder
Step 2: Chop and Strip Your Adapter
Step 3: Open the Handsfree Kit Up
Step 4: Carefully Unsolder the Old Connections
The best way to unsolder is to hold the soldering iron on the bare end of the wire for a bit and then give it a quick tug. But you knew that.
I can't tag the photo for some reason, perhaps because I use Linux, but you can see where the wires were, there are left, right, and two common pads.
We are going to bridge the common pads, because we only have one common wire from the adapter.
Step 5: Solder the Adapter On.
To stop the wires touching inside the adapter, they coat them in a coloured plastic skin. It's very soft and thin. Use a bit of very fine sandpaper/glasspaper between your finger and thumb to GENTLY scrape it off until the end of the wire is shiny and salmon coloured. Do all three wires - the one which looks bare isn't...
Solder the green to the left (pad marked L +), and the red to the right (marked R +). Solder the remaining salmon coloured wire to the common pads, bridge the two common pads with a heap of solder.
Step 6: Test It!
You could also make a phone call to test the microphone still works. But you have nobody to call... do you?
Step 7: Finished!
Optionally you could solder the leftover piece of adapter to the old headphones so you can still use them with your new handsfree kit. But why would you want to. I found it much easier and more satisfying to bin them.