1. A computer-implemented method, comprising: at a portable electronic device with a touch screen display, displaying a set of messages exchanged between a user of the device and another person in a chronological order; detecting a scrolling gesture comprising a substantially vertical movement of a user contact with the touch screen display, wherein the detecting of the scrolling gesture is substantially independent of a horizontal position of the user contact with the touch screen display; and responding to the scrolling gesture by scrolling the display of messages in accordance with a direction of the scrolling gesture.