What devices are included in the VoLTE for iOS?

If your Apple device is among the list, your device is eligible for VoLTE Pilot:
-iPhone 6S+, 7, 7+, 8, 8+, X, XR, XR MAX, XS, 11, 11 Pro, 11 Pro Max, SE (2nd Gen), iPhone 12, 12 mini, 12 Pro, 12 Pro Max