My current, admittedly old, phone (oppo Reno2 that I got second hand specifically because it was VoLTE and VOWiFi capable) doesn't work on the VoLTE or VOWiFi network with Mighty. 

I didn't realise this for over a month - the last time I received an actual call being the day prior to the shut off.

I was ready to get a new one (and likely will still have to) when I realised I was pretty sure when I first got it while I was on 2Degrees short term (after my Kogan plan expired) that I had seen it say "VoLTE" on the signal, so double checked and confirmed its a NZ phone (from Spark), with VoLTE. It's just that the toggle switches don't appear unless the network has provisioned these to my phone. So I attempted to use the manufactures menu to turn it on (there, but the toggles are greyed out off), and then used Pixel IMS to force the switches on (they now appear in the manufactures menu as greyed out on). But no dice. 

I then attempted to use my Mighty SIM in my even older Samsung A530F which the 3G text from Kogan kept telling me was not going to work on VoLTE - no dice. And my even older Huawei 3i Nova. No Dice. BUT it did tell me something interesting - all my most recent calls ( a bit confusing because I'm not sure if they were on the Oppo or hte A530F, or on 2Degrees or One, and the last a day prior to the One shut off) showed in the menu of both phones as being made over VoLTE - implying not only had it been working, but that both older phones were also VoLTE capable. 

So the next logical thing was to stick my 2degrees sim in the Oppo of course (not 100% sure I had used it in this phone prior, but likely)... and now I have VOWifi as an option in the regular menu and it works (still no VoLTE though. Kogan SIM shown neither). So I try the 2degrees SIM in the A530F - and I have both VoLTE and VOWiFi where Kogan and Mighty show neither. (I don't have a Spark SIM - but I have found a few online suggestions that both will work on the Spark Network. I may even go get one just out of interest)

So suffice to say I am a little annoyed that I have two phones that it would seem do in fact have all the necessary hardware and software, yet don't work on specific networks because of something on their end rather than mine (despite many people saying that there are no specific "whitelists" or provisioning on NZ networks)

Anyway I would be perfectly happy with the Reno2, and likely only going to end up replacing it with something around the same age and specs (well, slightly newer) and frankly would rather save the money. My Mighty sub rolls over tomorrow and I am left wondering if I should just ditch it for a potential working Spark one (though price factor on an unlimited/high data plan may make this ultimately uneconomical), try another (seems Kogan is out - who would be my next choice. And suggest its One network related). Or get a new working phone (likely the only actual option). 

Interested to know if there actually is a solve. "Support" gives the same "advice" over and over - txt the 3G number - even after I point out it just tells me that they didn't test my model, and show them it is VoLTE capable. As well as if anyone actually knows why/how many (apparently thousands of) people have had to shell out for new phones that may have actually been capable.   

If not any suggestions for similar Spark network plans? Or phones that you have also found that should, but don't, work that I should avoid (it seems similar aged oppo models are up there, along with a few others)