Twitter has hugely improved its mobile web experience by releasing an update that allows Twitter from a mobile browser to look a lot like its native apps. This web mobile experience will be available for all high end touchscreen phones, whether an official Twitter application is available for it, or not. It was built from ground up for smartphones and tablets and includes support for HTML5.
The new Twitter mobile web experience
It has functions like pull and release to refresh, tab switching and gesture control, which all works pretty well. It's a huge improvement from their previous mobile web experience.
Twitter is rolling out the new mobile web experience to a few iPhone, iPad and Android users today and to more users next week. It can be accessed by going to twitter.com on your mobile's browser. If you're not one of the few they've rolled out to, you can still access the old mobile web Twitter from your mobile browser.