I have had this very same issue where all of a sudden the person on the other end of the phone call can't hear me any more. Hanging up and calling back seems to be the only fix. However, I bought two of the GNEX phones on the day they became available in the US (one for me and one for my wife). Both of these phones had the issue and tech support recommended I returned both phones and thought new phones would address and fix the problem. After I returned both of our two original GNEX phones, immediately the two new GNEX phones started experiencing the exact same problem. So at this point we have had 4 GNEX phones expericence this "mic issue" so to speak where all of a sudden people can't hear us when talking on our phones. I have had SEVERAL long phone conversations with Verizon and Samsung about this issue and they keep playing dumb like they have never heard of this problem before. The one common denominator is our SIM cards were NOT replace, and our last Verizon Tech recommended that we go and get new SIM cards to see if this fixes the problem. I have also read this potential solution may work from many other forums. I'll go to the Verizon store tomorrow and get new SIM cards and see if it fixes the problem. I'll be sure to post and let everyone know what happens.