Have used Airtel as a corporate and private client in Bangalore. Their customer service is useless - left hand does not know what the right hand is doing.
First case: In 2012-3 during a number transfer from Airtel corp to Airtel private they actually gave my unique number off to someone else! When the actual approval came 2 months later(lost my paperwork multiple times) it was issued to someone else. It had a huge balance which was also misappropriated
Airtel data card - works only in some metros and not all - switches to such low speeds you would wish you did not order it - got a photon and am gliding smoothly on
Finally decided to get another card, got one from Hyderabad circle. Today jan 24th 2015 the ENTIRE hyderabad circle is down and in Bangalore since morning none of the cards from Hyd work in Bangalore - what a joke! Shifting to Vodafone after several missed meetings
Obviously the skin deep smile of Airtel says they dont care.
PS I am using a Photon to write this review:)! and it works when Airtel does not
The only real good part of Airtel is their zonal and regional escalations which work - but takes months to resolve.