It'll be good to know what the repair shop says. I've tried restarting mine so many times now. Calls from both directions. Battery in or out. Resetting to defaults. But not a hint of the microphone coming back.
It's great that some people are having luck with this, but I would be worried of the times it decides to stop working. Especially if you are on a call etc. Not the best to be worrying about it all the time.
I'll keep trying with resets etc, but I think I've ran out of combinations.