Steve Streza demos his iPhone Twitter client and explains why it almost certainly won’t ever be. It sounds quite interesting, though, and I think it has huge potential. For example:
On top of that, you can merge multiple timelines together, across all types of timelines, accounts, and services. For example, if you use Lists on Twitter and Facebook to organize, say, your family members, you can create one contiguous timeline which combines both those lists and shows you what your family members are doing, regardless of where they posted it to. Or, you can combine your Twitter followers, mentions, and direct messages together, similar to how Twitterrific works. This saves you time, as it lets you create your own timelines which show you new perspectives on your social networks that you simply can’t get with most Twitter clients.