1. A program stored in a memory of a mobile communication device and executed on a CPU of the mobile communication device, the program, when executed, functioning as a mobile communication device platform constructed on a mobile communication device on which a default application originally provided on the mobile communications device is operated, and an application execution environment on which a user setting application is operated, the application execution environment being configured on the mobile communication device platform, Wherein: the application execution environment has a function of providing a first software interface for receiving a first instruction regarding a wallpaper setting to be given to a wallpaper setting program operating, as a default application, on the mobile communication device platform, while a user setting application is operating on the application execution environment, the wallpaper setting related to a display content of the user setting application; the mobile communication device platform has a function of providing a second software interface for receiving a second instruction regarding the wallpaper setting from the application execution environment, the second instruction based on the first instruction; the application execution environment transmits the second instruction regarding the wallpaper setting to the mobile communication device platform through the second software interface in response to receiving the first instruction regarding the wallpaper setting through the first software interface; when the user setting application is not operated, the mobile communication device platform sets a wallpaper in accordance with a predetermined setting which is set in the wallpaper setting program operating on the mobile communication device platform; and a when the user setting application is operated and shifted to a paused state, the mobile communication device platform sets a wallpaper in accordance with the second instruction regarding the wallpaper setting, wherein the user setting application is shifted to a paused state in response to a notification generated upon occurrence of an event