For this new year Airtel is offering free Facebook access to its users. You can use any of the following urls to get it
Facebook.com
m.facebook.com
This offer also available for the Facebook application too.
There will be a cap of 30MB for a month and this service is activated already.
The official facebook page of Airtel says
Hi, we are offering airtel users 30 mb of free Facebook usage data per month (only through www.Facebook.com, m.facebook.com or Facebook Application.) till 31st January 2014.
Remember 30MB is not a big deal, but you may use it for free 
Read more here Airtel India Facebook page