You can also use something like QuickReader (http://www.quickreader.net) on the iPhone which implements the guide with a highlight or underline. You can copy and paste text into the app or download books from sites like Feedbooks.com.
I just released an iPhone app called QuickReader (http://www.quickreader.net). It is a "speed reading eBook reader" that trains you to read more words at once (expand your field of vision) and track properly. It employs the same techniques as are taught in the better speed reading courses. You take a speed reading test and then adjust the reading guide from 100 to 2000 words per minute. It comes with 21 full-length eBooks, so it doubles as an eBook reader. You can watch a demo video describing how it works at http://www.quickreader.net/videos or find it on the iTunes app store at http://bit.ly/GetQuickReader.