For this to be used very much, access has to be free, or close to free, or at least a fixed monthly cost, and not charged on usage.
Many schools in developing countries have no extra money to put towards this. Their costs for salaries, books, etc. are usually already insufficient.
In the USA and the developed world, Access is via telephone, or another telephone technology, like ISDN, or higher speed digital interconnects.
This is probably not feasible in developing countries for final access, for the reasons outlined above - namely usage based charges, and other expenses. If a school has a telephone, it is probably not for students use, costs by the minute, and is of poor transmission quality. However, like the rest of the world, once the messages reach a local town, they are best transmitted via telephone.
I propose using existing local transportation for the "last mile", where information is delivered like milk. Either this will be using high capacity removeable media, like ZIP drives, or via radio. Foe ease of explanation, I use radio in my description, referring to a Radio Telex. To use ZIP drives, these disks are simply carried to a local center, where outgoing messages are offloaded and put "on the wire", as a local center will have telephone service.