I think i saw dust accumulating within the earpiece (the place where sounds are emitted if you're not on handsfree) and because the earpiece gap is so small, i don't think so it's even possible to even try getting the dust out.
Further, i also noticed that there are several gaps as well when you open up the "door" on the top of the phone to charge it. If the earpiece have dust resides in it, i am sure dusts will get into the phone through the gaps at the "door".
My question is this, will this do harm to the phone in the long run and if affirmative, how to prevent =/
You can always use a computer air spray to remove the dust. You can buy a dust cover for the headphone jack on ebay:
(to prevent dust getting into the headphone jack port)