Cory Wilbur, a 25-year-old software engineer in Boston, never used to read much. He barely cracked a book in college and would read one or two a year on vacation, at most.

But in the past year, he's finished 10 books, including Dan Brown's "Inferno," Walter Isaacson's biography of Steve Jobs and George R.R. Martin's fantasy series "A Song of Ice and Fire." He listens to audio books in snippets throughout the day on his iPhone during his morning workout, on his 20-minute commute to work, and while he's cooking...