This document discusses different ways to build mobile websites, including using media queries, user agents, and user opt-in. It describes detecting the user agent string to redirect mobile users, using responsive design with media queries, and allowing users to opt-in to the mobile or desktop site. Responsive design allows a unified experience across devices but doesn't allow custom mobile features, while user agents allow tailored mobile content but separate sites. The document recommends using responsive design with media queries when possible and redirecting by user agent when different functionality is needed, while making it easy for users on any device.