Follow below steps:-
1. Make sure you own a Airtel Number to get this offer.
2. Now from your Airtel Number write SMS and type OFFER and now send this to 54321..
3. Now you will get a message from Airtel 54321 that your request for activation is under process, Thank You.
4. Wait for 3 sec and that another message will pop up.
"You have been subscribed to miss call alert service, free offer valid fro 2 months and blah blah".
5. So now enjoy this free service guys hope this works for you all if you like this and it worked for you make sure you like this post so that other Airtel users can take benefit of this useful post.