Frotz is a free interactive fiction app for the iPhone. I just played through Photopia on it just to test it out, and it works quite well. If you happen to get the free app, go to Settings > Getting Started. Getting started has “New to Interactive Fiction?” and “No, Really, Where Do I Start?” sections that are very readable and highly informative. It’s a great solution for people wishing to enjoy IF on the go, and for those wanting to get their feet wet in IF.