This website http://techlogg.com/content/view/188/1/ says to covert videos in 480 X 320 resolution because that is the iPhones native resolution, but on the Apple website the tech specs list it as 640 X 480. Which resolution should I convert them?
Where are you seeing 640x480 from Apple. The link below shows 480x320.
Sorry, now I see it. The display is 480x320, but it supports 640x480 formatted video. I'm not sure, but I think in order to keep files as small as possible, I would use 480x320.