A call transfer method applicable in a call transfer device for use in a vehicle controls a communication device to communicate with a mobile phone of a driver when a vehicle is started. When an incoming call to the driver is detected, it is determined whether the incoming call meets one or more predetermined conditions before a transfer of the call can take place. A pressure detecting device is installed under every seat for passengers and if the presence of at least one passenger is detected, the incoming call to the driver can be handed off to the phone of the passenger. If no passengers are being carried, other options can be employed in relation to the incoming call.