Why Airtel doesn’t works on my handset while my handset supports VoLTE?
Airtel is currently testing VoLTE supoort. So all handset are not supported.

Why Jio supported all the handset with VoLTE from day one?
Jio was free for first six months or more when network was in beta. So you can’t complain for anything.

Airtel is a chargeable network when VoLTE is launched. So to keep things under control as customer would complain in case of call drop/problems.

Airtel VoLTE is available in limited no of states i.e. Mumbai, Maharashtra, Goa, Madhya Pradesh, Chhattisgarh, Gujarat, Andhra Pradesh & Telangana only.

Currently on these handsets are supported by Airtel VoLTE:

Samsung Galaxy A5
Samsung Galaxy A7
Samsung Galaxy A8
Samsung Galaxy A9
Samsung Galaxy J2(2016)
Samsung Galaxy J7
Samsung Galaxy J7(2016)
Samsung Galaxy J7 Prime
Samsung Galaxy J2 Pro
Samsung Galaxy ON8
Samsung Galaxy ON NXT
Samsung J7 Nxt
Samsung J5 Prime
Samsung S6 Edge
Samsung S6
Samsung Tab A
Samsung Tab A(2017)

iPhone 6
iPhone 6 Plus
iPhone 6s
iPhone 6s Plus
iPhone 7 Plus
iPhone SE
iphone 8
iphone 8 plus
iphone X

MI max
Mi 5
Redmi Note 4

Gionee A1
OnePlus 5

Oppo F3
Oppo A71
Oppo F3 Plus

Vivo Y55L
Vivo V5
Vivo V5s
Vivo Y66
Vivo Y55s