I will try to keep this post as small as possible.
This will enable Volte for Phone ranging from Lg g8x, g8 and V60 without root or modifying the system files.
Many have posted ways to get it, Iam only trying to help out the small bits missing for enabling on carrier without MBN in the LG phones.
1)First remove the sim from phone and then head to the phone dialer .
2)open field test menu under *#546368#*'your model number'#
3)open IMS setting(If does not open or shows only LG IMS without carrier and country , then insert sim enable universal enabler under field test, create a new config and select the 4 last options and restart phone without sim )
4)back to Field Test, IMS setting enable the below options:
4.1) under subscriber enable for IMS,ISIM, USIM
4.2) Under Xcap\Ut. Under General= enable UT,USSD Over IMS
Under ETC enable 'Check IMS Registration', 'Use rule-ID from response', 'Query on bootup'
4.3) Under GPRI VoLTE/VoWIFi enable VoLTE, ViLTE,VoWIFI,VIWIFI
4.4) Under test : Preference Operator can be set as 'OPEN' or your carrier short name. Really does not make difference for some operator , some do require it to same name as theirs.
Preference Country this is important as this decides if VoLTE gets enabled, Find your country short code example USA is US , India is IN. Find and try different short codes.
Enable:- 'support Volte AT command', VoNR, 'UAC Enabled', 'VoLTE Setting Enabled'
5) Go to Phone settings, Under network , APN settings add APN :-
APN name = ims
APN = ims
APN TYPE = ims
6) Save APN and make sure it shows under the APN names, Head back to field test menu under *#546368#*'your model number'# , open test , IMS setting and the press 'restart IMS process' wait for 1 min or so , see if the VOLTE icon shows up in the top of phone.
Points to keep in mind:
*#4636#*#* wont show registered sometimes, that's ok as long as you can make a call with HD written on calls or , if during the call it is 4g or LTE. provided VOLTE icon shows always on top of phone.
If in case VoLTE disappears at any point, no need to go through all these steps , only need to go to field test, under IMS setting , do 'restart IMS process' .
Vowifi is not confirmed, IF someone does get it please share their Operator name and preference country short name.