The only way to remove the dust is disassemble the phone
it's not easy, i searched a bit on google and found a youtube [http://www.youtube.com/watch?v=dE81IaQHEHc|video] showing the procedure.
to clean it, you need (latex/medical) gloves and some tools to clean camera lenses (search for Zeiss Portable Lens Care System - maybe you will find a similar set - i've chosen the zeiss set because it's easy to google it)