Also at the decentralized bitcoin exchange site LocalBitcoins.com people trade with various alternative payment systems, including Kenyan M-PESA. Because at LocalBitcoins.com trading happens peer-to-peer (no centralized accounts) the site can support almost any payment method the users can throw at it.
Which brings me to the point... Nigeria is not behind, but might be actually a forerunner. There has existed some bitcoin trading in Nigeria for some time now:
Supposedly bincoin is good for traditional Nigerian online businesses?
(disclaimer: I am working with the project)