The Google Webmaster Central blog has two excellent write ups on mobile SEO concerns and techniques. One is named Help Google index your mobile site and the other is named Running desktop and mobile versions of your site.
The reason for the two different articles is that often webmasters consider smart phone enabled sites as strictly mobile sites, but there are many mobile phones that have web browsers that don’t provide the rich experience that an iPhone or Android device do. If a webmaster wants to optimize their site for those devices and submit this type of content to Google, they can by learning how to create mobile friendly web pages for those devices and submitting a mobile sitemap.
At the same time, many webmasters prefer to not have a new URL for the same page based on accessing it on a desktop, iPhone or old-style mobile browser. Google’s second blog post explains how you can use the useragent to display a different stylesheet for showing the same content, in a different layout, for mobile devices and desktop devices. Google offered a diagram explaining how to do this without being considered cloaking:
To be honest, the best practices in this area are not 100% clear to me and I don’t think it is 100% clear to Google either. There are just too many ways to handle mobile devices, with so many different mobile browsers to use, plus handling printer friendly pages, desktop based pages, Internet Explorer versus Firefox or Safari and Chrome. Building out web sites that also comply with Google’s guidelines is complex, especially in the mobile front. These mobile blog posts from Google are useful but I, as do many, still have questions about handling this properly from a search spider perspective.
I actually have a clear write up on how I handled this for my corporate site on the Search Engine Roundtable, but like I said, there are multiple ways to achieve a mobile friendly site and comply with Google’s guidelines.