BYOD, as in Bring You Own Device, hence buying and importing phones that you wouldn't typically see on a Telstra plan.

Whether or not a device can actually support VoLTE unfortunately actually has very little to do with what is and isn't being blocked; even the industry itself doesn't know what 100% will and won't be affected, as there are devices that are told to be ready for post 3G shutdown, but in testing they are not emergency VoLTE ready, and so will not be able to make emergency calls after the shutdown, and no matter what you put on the phone, if the IMEI number isn't on a compatible registry, that phone will be blocked.

I do highly suggest reading the article, as it does go more into depth on everything (as well as the Change.org petition). I am "tech aware," to a degree; however, I am not at all well knowledged, just something I genuinely very much feel needs to be shared.

No. This includes 4G and 5G devices. 3G devices will just stop working when the 3G network is shut down and don't need to be blocked.

My phone is set to LTE only in my modem config, all of my calls are via VoLTE, my phone will still be blocked.