I got an "OEM" dock assembly from ebay.
The ribbon cable connecting the assembly to the logic board was slightly too long and therefore forced the connector in the ribbon to partly pop out of the logic board connector. That resulted in loss of mic and dock port in my case. Maybe in just affects the mic in your case?
Try opening the phone, put preassure and put preassure on the connector. Then call someone and see if it works...
Oh, this involves opening the phone while it's powered on... Do at your own risk......