
In 2005 Acacia published an
atlas full of fantastic maps on this topic.
Acacia is an information and communication technology initative in sub-Saharan Africa. The map shown here is a measure of the ICT Opportunity Index, which combines "ITU's Digital Access Index and Orbicom's Monitoring the Digital Divide/Infostate conceptual framework and model."
Page 16 also has a great map on the affordability of the internet in Africa.
I'd love to see this updated - it's the most comprehensive mapping of internet and telephony infrastructure and access that I've seen.