I am in J&K and I put the sim in
iPhone 6S and it's changing from 4g to 3g when calling. i didn't got any carrier update too.
I hope airtel doesn't fcuk up though. as their 4G network is very stable to be honest(even though it's not VOLTE). I do gaming on PS4 , and on mobile (GAMELOFT) and both are rock solid compared to BSNL broadband with low pings and JIO which is pathetic anyways even with high speeds JIO latency and pings to ps4 gaming and mobile gaming is garbage.