Matt Cutts gives clear instructions on how to deal with duplicate content on a mobile site His prime suggestion is to create a subdomain like m.mysite.com and adjust robots.txt to allow only the googlebot-mobile to access the files. You can block the mobile bot on your main site. Create a Mobile Sitemap and submit it to Google to inform us to the site’s existence.
More information can be found on Google Webmaster Blog
Filed under: Duplicate Content, Mobile SEO