Quick follow up - I can confirm Band 20 is a GO!
I enabled 'LTE Only' in the hidden menu, and found somewhere with the correct signal mix. I made a 4G voice call and can see 'HD' in the dialer - see the screen grab.
******Warning! Follow these instructions at your own risk. I am not responsible for any damage done to your phone*********
Just got this working on my GS4 and .........
I got this working great on my i9505 S4 with the most recent 4.3 UK releas...
On 5.3.1 it took about 9 attempts to work, trying the windows kingroot program, and both kingroot versions included in the supertool.
The one that finally worked was the one installed by the supertool when choosing for version 5.3.1 .
The main i...
Thanks for the feedback.
Which method did you use to get root and is it reversible?? (My banking app wont work on rooted phone!)
This one - my bootloader is unlocked. http://forum.xda-developers.com/g4/general/howto-complete-guide-to-unlock-tw...
Sadly I can confirm that VoLTE doesn't "just work" on non three supplied G4 with this firmware.
Keep us posted with how you get on with the hack!
So I hexedited the mmcblk0p22 as described by michalpro in this post, and conclusions...