66% of Facebook mobile users in India access via a feature phone

"When you think of how people access the Internet, you might glance at your smartphone or computer and imagine everyone around the world using similar devices. However, roughly 7 out of every 10 people in the world, many in high-growth countries like India, Brazil, Indonesia, Mexico, South Africa and Nigeria, use far simpler devices, like feature phones, to access the Internet.1
The rate of people using only mobile devices to access the Internet is skyrocketing, especially in high-growth countries. More than one billion people access Facebook on mobile every month and many do so across multiple mobile devices. In many countries, a majority of those people experience Facebook on a feature phone: in India 66%, in Indonesia 71% and in South Africa 68%."
Source:  Internal data from Facebook, cited in a blog post, 2nd July 2014

The top 5 countries for Facebook users

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Source:  Economic Times, 8th April 2014

The number of Twitter accounts by country

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Source:  Data & Analysis from Semiocast, published 30th July 2012
Note 1 - more data in the full article
Note 2 - These are obviously just estimates (from July 2012), not official figures