Make a web page open at the desired size at an iPhone.

This suggests what one may enforce a screen width at an iPhone with the following metatags:

<meta name="viewport" content="width=device-width">
<meta name="viewport" content="width=320">

 
 

I have tried it and it works. However, if I turn my phone from portrait to landscape I would like the 320 setting to turn into a 480 value. How may I have this happen? This suggests there is a way with JavaScript. I have not tried it yet.