We predict that there will be a lot of Twitter interfaces for the iPhone. This is the first we've seen, though: Hahlo. It's not crystal clear what its icons do (the star is what you use to creat a Twitter message, for example), but it should take you all of two minutes to get the hang of it anyway.
iPhone link: http://www.hahlo.com/
Web site link: http://www.hahlo.com/
Via Frantic Industries.