By no means have I proven this to be a hard and fast issue but I have encountered this a few times now.
I have noticed on occasion that when I have the phone recharging and a phone call comes in that the person on the phone has trouble hearing me until I disconnect the charger. Interestingly, this doesn’t happen when I have the Samsung Galaxy S III recharging in the car and I use the Bluetooth hands free in the Prius.
Admittedly, I am not using the provided charger at my desk at work to recharge my phone when I have observed this issue but this problem has also occurred when recharging over USB at my desk at home. It would be interesting to know if others have run into the same issue and whether or not this is a hardware or software issue.