klark0 - 4:42 pm on Dec 28, 2012 (gmt 0)

Google published some guidelines a few months ago. Although they prefer a responsive design, they do support and recommend "Separate URLs for mobile".

Highlights:

On the desktop page, add a special link rel="alternate" tag pointing to the corresponding mobile URL. This helps Googlebot discover the location of your site's mobile pages.

On the mobile page, add a link rel="canonical" tag pointing to the corresponding desktop URL.

[developers.google.com...]