I am using the below Airtel Top-up and i know they exist.

LOC A2A @10paise for Rs.65 Rental - All local Airtel to Airtel Call charges at only 10 paise
22000 Local SMS Free @Rs.60/PM - 22,000 Local SMS Free per month.
2 GB GPRS Free @20KB/30Ps With Rental Rs 98 - 2G GPRS Plan with rental Rs 98 for 2GB data download

Share anything else you may know.

Cheers!