Here is the procedure to check the 2G data usage balance for all telecom operators.
Please let me know through comments if there are any mistakes in the list.
Aircel: Dial *111*10#
Airtel:Dial *123*10#
BSNL: Send SMS DATA2G to 53733
Tata Docomo(GSM): Dial *191#
Vodafone: Dail *111# and select option 6
Reliance (GSM): send SMS BBAL your mobile number to 53535
Idea: send SMS USAGE to 58880
Videocon: Dial *123#

source:http://www.worldofgprs.com/2013/04/procedure-to-check-your-2g-gprs-data-balance-for-all-operators/?utm_source=feedburner&utm_medium=email&utm_campaign=Feed%3A+WorldOfGprs+%28WORLD+OF+GPRS%29