Interestingly, outside the "1st world" mobile phones are quite common. The speed at which this technology trickled down is amazing, about ten years from yuppies in major cities to subsistence farmers in failed states. Even more amazing is penetration. Most things just don't go that far down the economic ladder at all. Basic, fundamental things like vaccination, artificial fertilizers, electricity or regular phone lines which our grandparents took for granted have been outpaced by mobile phones in many places.

Tablets may be similar enough to mobile phone to hope that the same economics apply and we might see the <$3-a-day majority benefiting by 2020. Hopefully.