First of all, the term Free isn’t true. You have to do a one time recharge for Rs. 1,450. So technically, Free data isn’t true.
Second, there is no unlimited data. There is a data cap of 30GB. After that, your data will be reduced to 64 Kbps.
To compare this offer with Reliance Jio’s 4G offer, you will still be paying around Rs.50 for 1GB of 4G data. But again, it’s not anywhere close to Free.
This is just AirTel’s way of playing with words and doing a marketing gimmick.
According to a TOI report, AirTel claims that what is actually free is the 64 Kbps sluggish speed internet you get post FUP limits.