Answer to: Microphone not working when making/receiving calls**THIS SOLUTION WORKED FOR ME, BUT MAY NOT WORK FOR OTHERS** I was having the same issue and couldn't get it to work AT ALL. So for whatever reason, I decided to use my digital caliper to measure the screw. For anyone confused, the screw that is spoken of, is the screw that is on the FAR LEFT of the Wi-Fi EMI shield right below the camera. The screw measured at 2.5mm instead of the factory SUPPOSED measurement of 2.3mm. I switched out the screw with one that DID measure at 2.3mm and it completely and permanently fixed the problem. I spoke with an Apple representative two months later when I was sure that the problem was fixed, and they told me, "we're well aware of the problem and anyone with an iPhone still under warranty, may turn their iPhone 4 in to be repaired or replaced." I know it's extremely stupid that this was a "valid" response, but I hope this helps!