14-05-2018 16:59 - edited 14-05-2018 17:00
What I see on the 4G super-voice page is P20 Pro is not on the list. Using an unsupported device can cause undefined behaviour. It could be the device won't let you use it or the device lets you enable it but does not work or the voice calling function becomes broken etc.
16-05-2018 23:26 - edited 16-05-2018 23:34
Thanks again @evantkh I took the phone out to a rural building which was in a band 20 cell and in line with 3's position that the P20 IS supported but that the process is automatic, So I WAS able to make very clear 4g calls inside, and access the internet on 4g with no drop to hdsp+ but with no special icon just the 4g and lack of a h+ icon.But with no way to force, enable, or otherwise test.