Ulysses is now out for the iPhone. Having used it on my MacBook for a couple of weeks, I might still be swayed by the shininess of a new tool, although it is one of the best writing tools I've used.
I'm still on the fence about using my phone for writing though, but if it writing on your iPhone is your thing, it may be worth checking out.
I call Ulysses a writing environment, though not really a publishing environment (more on that in a bit), because you're surrounded with a rich set of writing tools. Put another way, it's one of the very few apps that feels relatively complete. That doesn't mean it isn't finished or there's nothing left to fix or add. It's more that Ulysses leaves me with the fewest questions, frustrations, and frictions of any writing app I've used.
— Review: Ulysses 2.5 for iPad and, now, iPhone by MacStories