Check Your BSNL DataOne Usage
Tech Rokr has mentioned how you can keep track of your BSNL DataOne usage. BSNL provides your usage statistics on its portal @ bbservice.bsnl.in. So before you enter that website, you need to request a 14 digit portal ID. You can get that 14 digit portal ID by calling 12678 from your BSNL landline phone. Ask the person to give you your 14 digit ID number.
Once you have that number, visit the bbservice.bsnl.in, and you will see link called "My Services". Once you click on that and follow the steps to find out your BSNL DataOne usage.