The interface will eventually replace the standard mobile site for Twitter, though it is still under development. Users of the BlackBerry browser and some other phones have reported issues with the new site. Ultimately, the new interface may supplant standalone applications on phones as well, which would make Twitter even more portable.
This latest development comes as Twitter seeks to turn a profit, introducing paid accounts to their business model. While their financial future may be in question, many sites and businesses are embracing the service, and being more accessible on mobile devices will help fuel that.