There are many dynamic things to do work with DPI if you don't care about DPI You can simply use stage.scaleMode = StageScaleMode.ShowAll.
If you set it what will happen is Swf stage come to center of the mobile screen and scaled propertionally.
based on the mobile screen dimentiones it will scale only one Width or Hight, so in ur swf you should have small extra safe area beyond the stage size.
Our project with same concept.
you can test with any mobile screen it will not show any gaps or borders
Hope this will help you.