When you take the phone away from your face, the screen should turn back on. From there you can hit the End Call button.
Before I lock the screen from last use, I close all the apps. Tap the home button to go to the main scree then hold the mechanical home button for 2 seconds then select Remove all. Next time you unlock the phone you can go to the phone or contact icon to make your call.
Yes you have to go through a similar process on iPhones as well.