Hibino:[snip]
My phone is capable with VoLTE but is not allow by Spark
This is simply not correct. NZ Telcos do not allow or disallow devices on their networks, other than specific blacklists and TAC locking for some devices.
In respect of VoLTE, it is up to the device to have the settings for the carrier you wish to connect to. This is the carrier profile. It is not that Spark disallows the device, but the device doesn't have the right settings for Spark.

