Prepaid customers on Airtel have an option to ‘loan’ Rs. 10/- if you are running out of balance and have no recharge options handy. Type ‘LOAN’ (without quotes) and send SMS to 121. The mobile will be instantly credited with Rs. 10/- talktime. At the time of next recharge, Rs. 11/- (including Re. 1/- service charge) will be debited from your normal credited balance.