As you can see at SAP note 1093513 , "... SAP does not support specific browsers or devices of specific manufacturer. If device-specific functionality is required (like i.e. function keys), ITSmobile provides a procedure to include device-specific META tags or Javascripts. ..."
You can use the following code excerpt to capture the onkey command of function keys and have it submit the respective okcode command: 
It is not guaranteed that a function key will work, since the device needs to allow it too.