THE BASICS
SPECIFIC DESIGN
While the first two methods are only concerned with the web aesthetics of the website, creating a mobile-optimized site is the only way to truly address the contextual needs of a mobile user. By using a sub-domain of your main site, or a unique domain all together (.mobi domains are currently available for mobile sites), you can specifically target mobile users.
Mobile-centric pages are usually adaptations of their sister sites utilizing content specifically useful to users on the go. "Overall, pages are usually leaner, sparing excessive data costs and resulting in a faster browsing experience" 1
While there are certain disadvantages to this method (maintaining two sets of files for each site, hoping your mobile audience uses the correct URL), the advantages of keeping a mobile site contextually relevant and creating a positive experience certainly get my vote.
1 Moll, Cameron, "Mobile Web Design," http://www.mobilewebbook.com.

