There maybe a way. Download the firmware seperately. once done put your iphone into recovery mode by turning it off completely and then hold the home button and then connect it to itunes. Keep holding till you see the recovery logo. on itunes it'll mention that your phone is in recover mode then SHIFT + CLICK on restore and select the firmware and let it install. Make sure that the sim (Airtel or Vodafone) is inserted before you do this. After it reinstalls the firmware and if this method works it will mention that a carrier update is available do you want to update. click on yes and that should be it. I have no clue if it'll work or not but give it a shot.
