the reason this is classified as a "Smartphone" is because all of the other features (Internet, apps, etc.) are just as important as the phone feature itself. Thus the phone is not a centralized feature that needs to be immediately accessible.
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I agree that it is easy enough to hang up the phone. That being said, i must disagree with you. You forget that it is a smartPHONE, hence it is a PHONE with other capabilities. The reason that it is "lacking" is because it is a touch screen phone. Smart phones of the candy bar type have a dedicated answer and hangup keys that always function in that manner no matter where on the phone you happen to be. On a touch screen phone, your UI changes with each application and in our case, each app is often designed by a different person. That leads to a complicated user experience.
That being said, if you dont have the brain resources to make a few on screen selections, what do you want with a smart phone anyway?