Twitter says that they built the new app from the ground up and was optimized for the latest mobile browsers supporting the latest technologies including HTML5. "It's rich - it takes advantage of capabilities that high-end device browsers offer, such as touch gestures and a large screen. And it's simple - it's easy-to-use and has the features you'd expect from a Twitter application, including your timeline, @mentions, messages that you can read in conversation view, search, trending topics, lists, and more."
The new Twitter app will make the mobile version of the service look exactly like the desktop version, but only a few Apple iPhone, iPod and Android users will be able to see it now. More phones will receive the upgrade each week; until the upgrade is received, users will continue to see the old mobile version of Twitter.
source: PCMag via ReadWriteWeb