I live in an area with marginal cell coverage at best, so recently I decided to buy some new phones that supported wifi calling. I (perhaps naively) assumed if the device was included on Spark's list of compatible devices and purchased in NZ (in this case, from OPPO's online store), it would work (despite the buy-the-phones-from-us CYA note all network providers seem to include).

However, despite being able to enable the features on both a Reno 8 Lite and A78 5G, neither VoLTE nor VoWIFI work on either phone.

I chucked a mate's 2degree SIM in and immediately both features work just fine, so I'm probably going to just migrate to them. My curiosity is thus: I noticed when using the 2degrees SIM that a specific option (whether to prefer mobile or wifi calling) disappeared from the settings. I don't know much about how the functionality works, but this implies to me that the network pushes some sort of configuration to the device OTA, which made me wonder: does even being able to enable the wifi calling option with my Spark SIM in at least indicate that the feature should work? Or is it just a case of the device being locked out because it's not a Spark-specific ROM?