I am on my second S5 and both have had the same issue. The person on the other end of my phone call can not hear me. I know the issue is with the microphone. The other day when speaking with my father, he complained that my voice kept cutting out. After connecting to my cars bluetooth, we were able to complete our conversation. I don't have a case on the phone so I know that's not the issue. I activated my new S5 four days ago and I am running into the same issue. This is really annoying!!!