phranque - 10:39 am on Sep 3, 2012 (gmt 0)
you should first read the Delivery Context section of w3c's Mobile Web Best Practices 1.0:
to keep googlebot happy (and most importantly to avoid looking like you are cloaking), you should probably read this from the webmaster blog, which should truthfully be titled "Making Websites Googlebot-Mobile Friendly".
Official Google Webmaster Central Blog: Making Websites Mobile Friendly:
and more - Official Google Webmaster Central Blog: Recommendations for building smartphone-optimized websites:
and this which also discusses the difference between smartphones and feature phones...
Building Mobile-Optimized Websites - Webmasters - Google Developers:
(this is probably just a subset of the information linked in travelin_cat's post above)
this WebmasterWorld thread might have some useful discussion.
Mobile website design - HTML forum:
it looks like these days the best technical solution is one url, media queries, responsive design.
i think your implementation will depend on whether you care if google indexes your mobile content and how you are going to treat a googlebot visit vs a human visit.
assuming you want to avoid problems related to cloaking, duplicate content, and non-canonical urls...