called the Apple store for tech support. said your phone is not suppose to get hot at all. maybe warm with wifi, but mine gets hot while on calls...very uncomfortable. on the phone waiting for tech support as i type this. its getting too hot.
since you just bought it, you might wanna think about going back to the store where you bought that and exchange it, it is not safe to have the phone that hot when your talking to someone.
just exchange it and get a new one