ZTE Warp, the screen will go black after dialing and not come back. No buttons will work. Have to remove the battery and restart the phone. Doesn't happen all the time but sometimes it will happen all day long. Some days not at all. I have viewed other threads on this forum and many say that the case can sometimes cover the face sensor. That is not the case here because I can remove the case and anything that could be block it yet the screen will not come back from black or respond to anything. Power button does nothing either.