Most mobile phones/cellphones have a rubbish proprietary adapter for which they supply some terrible headphones hard-wired into a handsfree kit.
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
You need the two items pictured below. The first is a handsfree kit which comes with your phone. It has a remote bit on it with a volume control and a microphone. It also has a Mini-USB plug, and some dreadful headphones.
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
Chop your adaptor in half with pliers. Strip the socket end to expose three wires (left, right, common). Optionally strip the other half if you want to stick the old headphones onto it for some obscure reason.
Step 3: Open the Handsfree Kit Up
Crack the case on the handsfree bit open. I just shoved my nail into a gap I found and slid it along until all the clips popped open. Your mileage may vary... Find a way to get it open ;)
Step 4: Carefully Unsolder the Old Connections
Find the headphone connections (they're connected to the headphones!) and unsolder them.
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!
This step is easy. Plug it into your phone, connect your posh (ooh look at mine they're Shure...), stick a movie on or a piece of music, and check you get left, right, stereo, volume control...
You could also make a phone call to test the microphone still works. But you have nobody to call... do you?
Step 7: Finished!
All working? Great! Clip the case back on - in my case I ensured a small length of my adapter wire was inside the case so that it was a tight fit - I'm not sure my abominable soldering could withstand the tugging that headphone leads get, luckily the wire was a little thicker than the original wire, so it's tight and rugged.
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.