To end a call
Simply tap the End button
on the Call screen to end the call.
If you accessed other device functions while the call was in progress, there are several ways to return to the Call screen to end the call.
Tap the Home Key
(in the Front Touch Keys bar),
tap the Phone Key 
(in the Quick Keys bar), then
tap the End button on the Call screen.Tap the Home Key
(in the Front Touch Keys bar),
tap the Contact’s name or number at the top right corner of the Home
screen, then tap the End button on the Call screen.Drag the Notifications panel down, then tap the End call button
on the Call screen.
NOTE
You can also press the Power/Lock Key 
on the back
of the phone to end the call, if you activated this feature in the
Call settings menu.