An integrated mobile terminal device including an external display unit, a personal digital assistant (PDA) unit and a cellular phone unit combined with one another, and a timer controlled by either the PDA unit or the cellular phone unit for enabling the PDA unit at given time intervals is provided. The cellular phone unit controls the external display unit in an enabled state, directs the PDA unit to control the external display unit when the cellular phone unit is switched off and the cellular phone unit detects the PDA unit to be in an enabled state, and transitions to an off state after activating the timer when the PDA unit is in a disabled state. The PDA unit determines whether the cellular phone unit is in the off state when the PDA unit transitions to the enabled state, and transitions to the disabled state after activating the timer when disabled.