faulty iphone spares or repairs *

hi here i have my iphone 3g ive had this phone for ten months and bought it brand new it is still under warranty but i cant find the receipt the button at the bottom of the screen is sticky and it has a few scratches and a small crack on the screen that is barely noticeable it works fine and sends and receives texts/phone calls and does games no problem phone calls only please as i have no credit