I recommend tweaking text-sizes, margins and floats through a dedicated CSS rather than forcing my user to view a totally new experience. Scaling the viewport means (for most sites) realigning a lot of things, especially menu's and padded content to fit in the frame.
Use this:
<link media="only screen and (max-device-width: 480px)"
href="iPhone.css" type="text/css" rel="stylesheet" />
Use this: