Have you already made the correct guess? Do you have something commercial in mind or you possess the spirit of freedom in software?
Either way, I think you are going to enjoy the new iPhone App: WordPress 2. I was actually merging the applications from acount to acount when I stumbled upon this gem.
The most prominent feature I love is moderating comments. Finally turning iPhone into a road journalist’s lover.
Suffice to say, in the terms of browsers, this blogging tool is like Google Chrome (Yes, I am using it on my Mac as well) – with everything essential yet holding a mini footprint at the same time.
Update: There is a blog entry on the official WordPress blog here