Recently I found that you can check BSNL broadband usage through sms. For that you have to do following steps

STEP 1 : First register your Landline number by sending following sms 52295(+919448077777 for Non BSNL Users)
Code:
 REG<space><STD Code><Landline Number> to 52295(+919448077777 for Non BSNL Users)
For example:
Code:
REG 012272123456.

STEP 2
Now you can check usage, for checking Broadband usage send following sms to 52295(+919448077777 for Non BSNL Users)

Code:
 BBU <space><STD Code><Landline Number>
Example :
Code:
 BBU 012272123456.

Hope that is helpful to you!