Apple's UI for the iPhone is a study in inconsistency. No two apps behave the same or in a similar fashion, and the Springboard (home screen) is completely different from every app as well. In nearly every circumstance there is a third party developer out there who has outdone Apple's software. It's hard to find those programs however because what's in the app store is mostly garbage. 90:1 easily.

IMO, Apple need to rethink the UI and concepts for all their built-in apps. They need to really create the next step. Everything they're shipping right now just feels pre-1.0 and very unpolished and featureless. iPad apps were a move in the right direction, and it's not only the larger screen real-estate that allows for more versatility. Apple could easily employ a pop-up menu paradigm for the iPhone as well.

You can go obscure with gestures, but that's not a solution either. Like two finger click to bring up a menu. I'm not suggesting anything like that. But in Mail there's already a bar along the bottom of the UI. Put a bloody button on it that shows multiple options in a slide-up sub-menu. The two buttons on there now are single-function. The Edit button at the top menu bar (which is also always displayed) only allows you to delete and move messages - why not forward and marking? Right now I don't think there's any way to forward multiple messages.