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 many ways to return to the Call screen to end the call.
Tap the Home Key
(in the Touch Keys bar ),
tap the Phone icon 
(in the QuickTap bar), then tap
the End button on the Call screen.Tap the Home Key
(in the Touch Keys bar ),
tap the in-call box (at the upper-left corner of the Home screen),
then tap the End button on the Call screen.Drag the Status Bar down, tap the name (or number) next to current call in the ongoing call notification, then tap the End call button
on the Call screen.
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.