I have this same problem with my ZTE Valet. I've had it about a year. I know two other people with this same phone that have this issue, as well. I believe I have found a way to get the "hang-up" screen to appear out of the darkness. I speak a very clear "Bye" or "Good-bye" into the phone, and then that screen comes up, so I am able to hang up. I hope this helps!

I have this problem too. The screen becomes completely dark and unresponsive as soon as the call is connected. The other buttons are also unresponsive. This happens about 60 per cent of the time I receive or make phone calls. I can continue the call but to hang up I end up taking out the battery. Does anyone have a better solution?

Hi John. You just need to press the red bar on the screen to hang up the call.

If you do that but it doesn't work, try restarting your phone and then try again and see if you can hung up. Let me know if it works.