The phone goes black when I take it away from my ear...before I even have a chance to disconnect the call. Is it supposed to do that? My wifes phone does not do it.
Does this happen on calls that you initiate or calls that come in while the phone is asleep? If its only on calls that come in while the phone is asleep, that would be normal behavior. After a call comes in, the iPhone returns to the state it was in before the call. Also, as Tamara suggested, if you are using a case for the iPhone, make sure it isn't covering any of the proximity sensors under the top of the glass.