Experience as on 30 July :
Airtel is known for its unreliable VoLTE experience. If it works it works else it doesn't.
Not sure on what logic the backend activates VoLTE, but its just irritates.
Even on officially listed compatible phones it comes and vanishes.
Remove the SIM it has problems, Change the Device it has problems. I'm sure there must be some mapped logic for activation, but at the customer end its just an awful experience.
Support is helpless and customer is clueless.
The steps to enable VoLTE are also useless.