After u put the Sim card in and boot up the phone the first time, will have pop up ask u to restart the phone. (This will install the telco bloatware)
You ignore it and press the power off button. Then, you switch back on your phone again. Ta da! No telco bloatware!
When you do this, do you notice there's no more setting to turn VoLTE on or off? I can't seem to find this setting anywhere. Even going to the hidden menu and trying to turn it back on from there, it just says not supported. Got a feeling that if you choose to install the carrier stuff, it downloads certain carrier information to the phone also to enable VoLTE.