The UI module runs when a BlackBerry® device user clicks the icon for a BlackBerry device application from the Home screen and is used to interact with a BlackBerry device user. The UI module can contain a dialog box, a screen, fields, and other components.

For example, if a BlackBerry device user highlights a custom message in the global message list and clicks the trackball, the UI module should start and render the message content. If the UI module is not running and a BlackBerry device user attempts to open custom message, the UI module starts automatically. The UI module can also provide Reply or Compose message functions.