According to this work from the Lausanne Committee for World Evangelization, 2/3 of the world's population can't, won't, or don't read or write. The majority of the world are oral learners, not literate learners. Hence, our entire approach to sharing the gospel needs to be revisited with this reality in mind. Instead of handing out Bibles, or even just reading them aloud, we have to rely on storying, songs, proverbs, chants, and many other mediums by which people are formed and transformed. We still tell God's story and use scripture, but we have to do it in a way that people can actually get it!
This short book (like 65 pages) is really insightful and free. Here is the link to the PDF: http://www.lausanne.org/documents/2004forum/LOP54_IG25.pdf
If you have a heart for missions and seeing the lost people of the world find Jesus, I highly recommend you check this resource out. As I read it, I was shocked that I had never heard some of this before.