You don't necessarily need an app. When I am done with a call, looking at email or surfing the internet, I hit the power button and make the phone "go to sleep". No crank calling for me!!!!
:icon_ banana::icon_ banana::icon_ banana::icon_ banana:
I don't think it can lock the phone, but I use Not Call Log. It allows you to go somewhere beside the Call Log (I chose the home screen) when a call is completed.