For me the problem occurs on outgoing calls.
The person I am calling can not hear me. I hang up and call again and they can hear me.
Issue occurs randomly approximately 1 out of every 4 calls.
I'm using an iphone 3GS with IOS 4.3.3 installed using Optus network (Australia).
When the issue occurs the person at the other end cannot hear anything no matter how loudly I yell into the microphone. I'm not accidentally putting the phone on mute because it is not indicated on the phone that I have and it does not matter whether I am using the microphone headset or not. I'm getting sick of having to apologise to my customers for my phone not working properly.
I tried replacing my iphone 3GS with another iphone 3GS, restored it from my backup and using my original SIM card. Problem still occurs.
Since replacing the iphone did not resolve the problem it must be related to IOS, SIM card or cell carrier.
Anyone else experiencing the same issue?