IT happened to my husband among other things and he went to apple to swap it for a another unit. I wouldnt hang on to in and exchange it for sure.
his phone was having really loud vibrations while on the phone and out of nowhere (while on a call) the volume would diminish or echo without the volume being controlled.
I guess some units are prone to have issues in the beginning or a product release
I have been on a few calls now where the mic goes dead and the other person can't hear you. Called Verizon and the they are doing "some switch stuff" but rep said it might need to be exchanged. Will waity to see what happens and I'll post any updates.
I have been experiencing this problem too. People say it sounds as if I am a long way from the phone. No problem when using a bluetooth headset though. Been to see a Genius today and they agreed it is a faulty mic so are going to replace when they get stock.