Airtel lifetime validity recharge allows its prepaid users to keep their sim active for a lifetime. In most other cases, the service provider will deactivate the sim if you do not recharge it for an extended time. However, lifetime validity recharge bypasses the deactivation.
Airtel has two plans in their lifetime validity recharge.
INR 100 - (INR 81.75 talk-time, 28 days outgoing validity, lifetime incoming validity, no data).
INR 500 - (INR 420.73 talk-time, 28 days outgoing validity, lifetime incoming validity, no data).