Well my friend , i have a similar issue also ie; my microphone doesnt function while i try to place a call through my speakerphone. I could hear the other party what they are saying but they cannot hear me at all. I tried several ways but still couldn't resolve the issue. I contacted apple directly but they said that my iphone 4 is out of warranty and in order to troubleshoot the problem, they would need to sign me up on a $30 plan. I am still trying myself as its not guranteed, that apple would be able to solve the issue a 100%. Meantime you could try browsing through several websites on google that might help you sort it out yourself. GOODLUCK!!!