As I was talking with Mom, I would frequently rub my back against the pay phone as if I had an itch. At the end of our conversation, I would then put one hand behind my back, acting like I was scratching my back. With my hand still behind me, while continuing to talk as if carrying on a conversation, I would hold down the switch hook for a few seconds to disconnect the call. Then I would bring my hand back around in front of my body.
