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.