Facebook announced today that it has collaborated with mobile operators throughout the world to provide access to a new mobile version of Facebook for free. The new site is called 0.facebook.com, and you won’t be charged any data usage charges, if you are with one of their partnering mobile phone operators.
Reliance and Videocon have partnered with them in India.
From the Facebook blog:
It’s free: Thanks to the help of mobile operators we collaborated with, people can access 0.facebook.com without any data charges. Using 0.facebook.com is completely free. People will only pay for data charges when they view photos or when they leave 0.facebook.com to browse other mobile sites. When they click to view a photo or browse another mobile site a notification page will appear to confirm that they will be charged if they want to leave 0.facebook.com
You can go to the blog post announcing this to read details and see other countries and operators that will offer this service.