A method for operating an integrated interface of a PDA (102, 202) and a wireless communication system (104, 252), suitable for a device that comprises a PDA (102, 202), a wireless communication system (104, 252) and a battery, comprising the following steps: when the wireless communication system (104, 252) starts to operate from standby mode, the wireless communication system (104, 252) transmits a wireless-communication-system-state signal to the PDA (102,202), said wireless-communication-system-state signal being part of a first serial port (110,22) if the PDA (102, 202) receives the wireless-communication-system-state signal when the PDA (102, 202) is in the sleep state, the PDA (102, 202) is wakened, and the input source of an audio element inside the PDA (102, 202) is switched to the wireless communication system (104, 252) so that digital audio data is transmitted to the audio element of the PDA (102, 202) via a second serial port (112, 24) from the wireless communication system (104, 252) and outputted by the audio element; and when the wireless communication system (104, 252) continuously operates and the PDA (102, 202) does not operate for a certain period of time, the PDA (102, 202) is switched to the sleep state, wherein the device is suitable to be charged via an external charging cable, and the device further has an external charging circuit to charge the battery, and there is an internal charging circuit inside the wireless communication system (104, 252) to charge the battery, the method further comprising the following steps for charging the device: performing a small-current charging to the battery via the external charging circuit by using the external charging cable; turning on the wireless communication system (104, 252) when the small-current charging is being performed; and after the wireless communication system (104, 252) is turned on successfully, turning on the internal charging circuit for charging when a battery potential achieves a first predetermined value. when the wireless communication system (104, 252) starts to operate from standby mode, the wireless communication system (104, 252) transmits a wireless-communication-system-state signal to the PDA (102,202), said wireless-communication-system-state signal being part of a first serial port (110,22) if the PDA (102, 202) receives the wireless-communication-system-state signal when the PDA (102, 202) is in the sleep state, the PDA (102, 202) is wakened, and the input source of an audio element inside the PDA (102, 202) is switched to the wireless communication system (104, 252) so that digital audio data is transmitted to the audio element of the PDA (102, 202) via a second serial port (112, 24) from the wireless communication system (104, 252) and outputted by the audio element; and when the wireless communication system (104, 252) continuously operates and the PDA (102, 202) does not operate for a certain period of time, the PDA (102, 202) is switched to the sleep state, wherein the device is suitable to be charged via an external charging cable, and the device further has an external charging circuit to charge the battery, and there is an internal charging circuit inside the wireless communication system (104, 252) to charge the battery, the method further comprising the following steps for charging the device: performing a small-current charging to the battery via the external charging circuit by using the external charging cable; turning on the wireless communication system (104, 252) when the small-current charging is being performed; and after the wireless communication system (104, 252) is turned on successfully, turning on the internal charging circuit for charging when a battery potential achieves a first predetermined value. performing a small-current charging to the battery via the external charging circuit by using the external charging cable; turning on the wireless communication system (104, 252) when the small-current charging is being performed; and after the wireless communication system (104, 252) is turned on successfully, turning on the internal charging circuit for charging when a battery potential achieves a first predetermined value.