This is a great question that you pose. I think that some combination of hard copy books and e-readers or mobile phones would provide the most educational "bang for the buck". Providing hard copy books, especially donated books, has been proven to be cost effective at increasing education and literacy at a low cost. This does not unfortunately address local curriculum and language needs. However, local curriculum needs and local languages can make local procurement of high quality, hard copy books expensive. If we could find a way to combine hard copy books (even donated from the United States) for general library use, and combine this with locally procurred books and e-readers containing local content, that might provide the best of all worlds. The trick is to find the right combinations of educational materials and delivery methods and secure the financing.