I have a brand new 3GS, first time Apple user. It has been a little over two weeks now and this phone has made at least 10 calls on it's own. People will call me back and tell me they heard me going to the bathroom, walking around the house, talking during work in a meeting.
I have seen this problem reported on these forums so I know it's not just me or my phone. Apple better get a handle on this soon or someone is going to have a lawsuit on their hands.
Otherwise I love the phone, except it's making me paranoid...someone could be listing to me type right now.