Over 80% of Nigeria's Facebook users access via mobile

"According to Socialbakers, the countries with the highest Facebook mobile penetration are:
Nigeria: 81.2 percent
Brunei: 80.8 percent
South Africa: 80.5 percent
Malawi: 78.3 percent
Papua New Guinea: 78.3 percent
Namibia: 76.7 percent
Botswana: 76.4 percent
Zambia: 73.9 percent
Japan: 72.1 percent
Singapore: 71.8 percent"
Source:  AllFacebook, 8th May 2012
Note - this means the number who access via mobile as a percent of the total users - but the people accessing via mobile may also access on a desktop device.