1. A method, comprising: at a portable electronic device with a touch screen display: displaying a list of instant message conversations on the touch screen display, a respective instant message conversation including a respective set of instant messages exchanged between a first person and a respective other person; while displaying the list of instant message conversations, detecting a first scrolling gesture comprising a substantially vertical movement of a first contact with the touch screen display, wherein the first scrolling gesture is independent of a selection of any object; responding to the first scrolling gesture by scrolling the list of instant message conversations in accordance with a direction of the first scrolling gesture, wherein the detecting of the first scrolling gesture is substantially independent of a horizontal position of the first contact with the touch screen display and the scrolling of the list of instant message conversations is independent of a selection of any object; detecting a selection gesture on a particular instant message conversation in the list of instant message conversations; responding to the selection gesture by replacing display of the list of instant message conversations with display of the particular instant message conversation, the particular instant message conversation including a set of instant messages exchanged between the first person and a single other person in a chronological order; while displaying instant messages in the particular instant message conversation, detecting a second scrolling gesture comprising a substantially vertical movement of a second contact with the touch screen display, wherein the detecting of the second scrolling gesture is substantially independent of a horizontal position of the second contact with the touch screen display, wherein the second scrolling gesture is independent of a selection of any object; and responding to the second scrolling gesture by scrolling the display of instant messages in the particular instant messaging conversation in accordance with a direction of the second scrolling gesture, wherein the scrolling of the display of instant messages in the particular instant messaging conversation is independent of a selection of any object.