arunss 0 Light Poster

Am designing a web page for mobile browsers. I have a div (having id 'wrap') which is 320px width and margin:0 auto. My all contents including header is within this wrap div. When I view it on my desktop browser it is positioning in center with a width of 320px. But When I browse it on a mobile browser (iphone or blackberry), it is not fit to the full screen. It only placed in a small portion of the screen. How can I include a wrap div for positioning a page in fullscreen on a mobile browser?