How to use 2g/3g internet on airtel for free ?

 
airtel free 2g 3g , how to use free 3g on airtel mobile
Every now and then telecom companies offer schemes to promote their company, the latest offer that airtel has given is free 2g/ 3g internet
how to activate free 2g/3g internet ?

For 2g internet

*SMS 2Gfree
to 121

For 3g internet

*SMS 3Gfree to 121

you will be given 100mb of  free data 2g or 3g based on your choice for 1 weak !! enjoy !!