Bryson Meunier wrote a piece at Search Engine Land named Don’t Penalize Yourself: Mobile Sites Are Not Duplicate Content. The article basically explains that if you have a mobile web address, i.e. different URLs for your mobile content, with the same content you have on your main URLs, it is NOT duplicate content. He said, Google is smart enough to figure out your mobile content is not duplicate to your main content – because they are smart enough to know when to show you the mobile content versus the normal content.

He said:

A Sphinn thread has a comment about this from Sebastian who said:

Honestly, what I still don’t get is why are webmasters still creating different URLs for mobile content? Why aren’t they detecting useragents and showing a different stylesheet for those mobile handsets? I really don’t understand why bother with special URLs? I mean, yea, Google is smart enough to know a mobile URL from a non-mobile URL based on the content. But when someone links to your mobile URL, that link doesn’t help you as much as it linking to your main URL. I rant about this more over here and give pretty good examples of how this works.

Forum discussion at Sphinn.