Via The New Mobile SEO Strategy from SearchEngineWatch.com:
The end result of all this is quite simple. Google supports three ways of serving mobile specific content to users and have provided distinct recommendations for each.
When a mobile user requests a particular URL:
- Serve the same HTML as the desktop version of the page and use CSS3 media queries to change the look of the site (ideal).
- Serve HTML and CSS that is different from the desktop version of the page.
- Redirect a user to a different URL utilizing mobile optimized content.