Buy "w580i microphone" from eBay or mobile spares shop and fit it as follows...
1) Push nail under small bottom fascia piece and prize off
2) Take off black rubber piece covering microphone
3) Pull mic straight up from the brown board (it is only held in by 2 small connectors) - you may need to hold the board down with a small screwdriver as the ribbon connector is flexable
4) Push new mic in
If it still doesn't work, you may need to replace your keyboard membrane, as that routes all the mic data to the phone's processor. This is also a simple process, although you will need to remove the sticker beneath the battery and disconnect the keypad membrane connector before peeling it off (it is stuck on with 3M sticky)
Steve, May 2009
