I'm not sure about an iPhone app, but I can access the web-based program that we use from my Blackberry. It's not an app though, it just works through the phones browser.
I would like to find the same thing.....I would think some one would make this
Where I live we use a pen and paper then enter it in the computer!
I have not yet found one for fire reports, but there are several out there for PCRs.