I may be doing a number of things incorrectly but I don't have any clue at the moment.

I'm designing a site for mobile right now. When i view a draft online I have the browser set up to display the resolution I want to view it at (640x960) on the desktop. However when I view it on the mobile device, it's at a completely different resolution. I'm referring specifically to an iphone 4S. It's advertised as having a 640x960 resolution but it's not matching up to what i'm viewing on the desktop. What am I doing wrong? Thanks in advance.