Here are some of the Service Codes, Offered by Airtel India. I 'm sure lot of codes do exists, Just do comment on the missed codes. So that it would be added in the Post.
*123# Check Local Balance.
*123*1# Local SMS Balance.
*123*2# Gulf SMS Balance.
*123*3# Local Airtel to Airtel Balance.
*123*4# Roaming account balance.
*123*5# Monthly Balance.
*123*6# STD Call Balance.
*123*7# SMS(Local and STD) Balance.
*123*8# Gulf call Balance @ 7/min.
*123*9# Airtel to Airtel Night calling Balance.
*123*10# GPRS/EDGE Usage Balance.
*123*11# All in one balance.
*135*2# Activate Missed call Alerts.
*135*1# Deactivate Missed call Alerts.
*121# Balance, Offer of the day, Hello tunes, Do not Disturb Services.
*678# Hello tune menu including mobile search and Free zones.
*567# GPRS/EDGE Activation.
Contests : Dial 543217.
Hello tune : Dial 543211.
Airtel Live Services : Dial 543212.
Background Music : Dial 543214.
Song Catcher : Dial 543215.
