WordPress.com is an excellent choice on which to build your conference site for several reasons, including the inexpensive plug-ins that turn WordPress sites into mobile-friendly sites and instant apps. Top Quark offers several, including the Conference Plug-In ($35 by itself), which allows you to manage schedule and speaker information, and the Conference App ($399, including the Conference Plug-In), which converts that schedule to an app. If you only need a mobile version of your site, WP Touch Pro will only set you back $49.