Consider the rotary phone. Imagine the weight of the heavy plastic receiver in your hand. Now say, "Goodbye, Aunt Gertrude" and hang up. Click!
It's that clang that signified an indisputable irreversible end to a call. The satisfying mechanical definitiveness of it reassured you that the call was disconnected and you could say whatever you wanted about Aunt Gertrude. She would never know.
Modern voice technology can leave us less certain than the rotary phone. Is there a way one device can alternate between two mutually exclusive states based on a simple intuitive gesture? And can the form communicate the two functions in a meaningful way in each state?