According to a tweet exchange between @FAUX_SHO and @Medium, it looks like an iPhone app is on the way!

So far I like Medium (I’m @Darnell over there for what it’s worth) but creating content via mobile web is the complete opposite of the desktop experience (the latter which is awesome by the way).
Glad an iPhone app is in the works, but sad that no time table for it has been revealed so far.