I just did this last night (although it was up/down volume pressure pads that were broken) and I followed the guide below. The bit I needed to change includes the volume, mute, headphone jack and power button. It's all one peice of cable. I got my cable and tools off eBay for about £8. To change the hardware on the cable you just pull the old one off and stick the new one on. then just reverse the steps in the guide below to put i back together. iPhone 3G Volume Button Replacement