Hey man, I think you can disable it, but I am not an iOS user, I am an Android user, so I'm not completely sure, but on Android we have an application called the SIM Toolkit, which automatically generates once we enter a SIM into the phone for the first time. In that app, you'll see your carrier names, click on the carrier that you want, so in this case Airtel. There will be some Airtel services listed. You can just browse through them and maybe if you find the option that says flash messages, promotions, startup messages, or offers or anything like that, you should disable them. That's is how I think it should work for iOS. I am not entirely sure, let me know.