In the US, it is customary to begin and end conversations with salutations. This includes in-person, written word and spoken word. "Hello"/"Goodbye", or some variation (i.e. "What's up?!"/"Catch you later!", "Dear John"/"Sincerely", etc...) are standard for all congenial conversations. Hanging up a phone without addressing the other person is seen as rude, or something done in anger, by the majority of US citizens.
That being said, it's not entirely unusual for a superior to hang up on an underling after the necessary info has been obtained. Imagine, for instance, a situation where imminent danger was at hand unless certain information was relayed quickly. Exchanging pleasantries in that situation would be a waste of valuable time, and both parties would understand this. Similarly, there's no time for, "Hey, Jim! How's the wife and kids?", if you were in a business meeting and needed sales figures for a client. In fact, in a situation like that it would even be acceptable for the underling to hang up on a manager.
"Jim, I need those sales figures for XYZ company"
"On it, boss!" click!