For this trick u have to keep ur balance more than 50 rs. First send ur default message to activate ur GPRS.
Now make new connection> set APN as internet> set IP as 0.0.0.0 & port as 0000 {in opera}> set APN as airtelgprs.com(in cell).
Now send deactivation sms. U can also use smart browser. This trick will work for 10 to 15 days After that repeat the same procedure