I know this one is old but many of us don't know about this free offer.
Aircel is providing free unlimited 3g for one month. No trick its just a free offer by aircel.
But since it is free there is a limitation that is you can use unlimited 3g between 6.00 a.m to 9.00 a.m.
Check if aircel 3g is available in your area. To activate the plan you need to dial
*122*5*1# or *122*456#
After dialing the ussd code you will recieve confirmation message from aircel that your pack is activated for one month.
You don't wake up early in the morning? Don't worry just use your brain. Schedule your downloading with IDM(internet download manager) and use a software called "Reconnect" which will automatically connect your internet and you can shcedule it.
Enjoy your sleep with automatic downloading. :D