Does the phone blank when you put it up to your ear? If not, your proximity sensor may have failed. If that happens, it won't disable the touch screen and your face could be causing touch inputs resulting in your phone hanging up.
+
+
You can try using it in speakerphone mode to see if it still hangs up.
Does the phone blank when you put it up to your ear? If not, your proximity sensor may have failed. If that happens, it won't disable the touch screen and your face could be causing touch inputs resulting in your phone hanging up.