How To Do It-:
1) First of Recharge your phone with small net pack or 3 Days NetPack
2) Then when your recharge will be done then you will get a message from Airtel that your recharge has been done and also you will get http://airtel.in/free link.
3) Now open http://airtel.in/free link,then disconnect net and close the browser
4) After Closing wait for 2-3 hours and then call to Airtel Customer Care means call to 198
5) After calling when they receive just say them that my 3G net browsing speed is slow and this problem is from 5-10 days.
6) Now Browse internet till when you get this message from Airtel " Your Complaint Regarding Network Issue has solved "
7) Then switch off your phone for 10 Minute and restart after 10 Minutes Complete
8) Now again Browse till your net pack will 1-2 mb and your balance should be zero.
9) At last open your free site and it will open successfully and now
10) Hurray ! Your Sim will be Unblocked.