I have the same problem with my Samsung Galaxy 3. When I make a call I can hear the person but the person can't hear me, My voice recorder and my voice search does not pick up my voice. I sent the phone back to Samsung to have it fixed, they supposedly fixed it and sent it back to me. It worked for a bit and now it is doing the same thing it was doing before I sent it to Samsung to be fixed. I called Samsung and they were acting like they couldn't give me an answer as to why my microphone is still not working. I will now have to send it in for the second time, which I feel I shouldn't have to do because it should have been fixed the first time.
I will say that I ordered my phone online from T-Mobile and was thinking that the phones that are ordered online are the ones with the microphone problems. What do you guys think?