I had this intermittent issue where callers could either not hear me or hear static. I did a complete reload of the software and reset the network settings on the phone but the problem always came back. I finally got to the point where the problem occurred all the time so I decided to open it up. I removed the battery and the speaker/mic assembly to check for debris but I found nothing. I also could not find any liquid damage on the board. I reassembled the device and now the phone works great. The only thing I believe it could've been was that the screws may have loosened and the board was not grounded. I've seen this happen to laptops just from typical transport or movement. Just something to consider if you see this problem however if your phone is still under warranty, have Apple service it.