Iphone 7Plus experiencing "Call Failed" on Airtel Nnetwork

Dropped calls are normally an issue with either the carrier's network or an account provisioning problem.

You should first contact your carrier and discuss whether there are any network issues affecting your service and if not to have your account reprovisioned.

In order to test hardware on your phone, it would be helpful if you have an unlocked phone, to try a sim from a different carrier and see if there are similar issues. You could also try your sim in a different phone and see if there are any problems. Either approach would help identify the cause of the problem.

Since you're using Airtel, I'm going to guess that you are no longer in Dubai where you purchased the phone.

If you suspect a hardware problem, you till have to take the phone back to Dubai. The warranty will not be honored outside of the country where it was sold in most cases.

You will find that you will have an incredibly difficult time having it serviced or replaced in India. iPhones do not and have never had an "international warranty". Though it is sometimes possible to have a phone serviced or replaced in a country other than where it was sold, that is the exception, not the rule.

Search these forums for the word "India". Virtually every hit will be someone who is complaining of service being refused for a phone they bought elsewhere. The remainder are people asking if they can have the phone they bought in another country serviced in India.