I think that I was missing to read that someone posted about end a call by tapping the lock-screen button top of the iPhone, next to ear.
Every time I'll end a call, I always tried to end call by lock-screen button and it does'nt work.
My iPhone 5 has the last Ios 6.1.4. Is it cuz of it?
So, I cannot use the function to make it call ending by that, and istead use end call by double-click by two fingers.
I really thought that using lock-screen button was the best alternative!!!!!