[Galaxy S 4 General] kayyappan:
I am not a developer but a HW guy.

This applies only to i9505 international version with Qualcomm processor as tested.

Please note that whoever tries the following, upon failure and/or ending up with bricked phone(s), incurring any loss, implied or direct, resulting from the application of what is described in this post, including but not limited to time, warranty, update from Samsung including security updates, resources, financial or otherwise,etc., does not point a finger in my direction but, does so at his/her own risk.

(Hope I scared a few).

The unit that I used originally had XXUHPK2 - XST firmware.

Whatever given below are personally experienced after quite a bit of searching, testing and few near misses including SIM not being detected or infinite loops when searching for network to register due to my own experimentation with Modem and NON-HLOS files.

But I never once lost my IMEI as the method is fairly straightforward. Always God "ODIN" is there to the rescue.

This applies to those who do not want an "always on" Jio4GVoice app and prefer to stay with stock recovery. Of course custom recovery can always be installed.

I have used PI1_VOLTE_JIO FW available on this forum but had faced few issues related to calling out at times, more so when I travel long distance. If I stay put at certain places it always worked.

Now to the works:

1. Using ODIN install I9505XXUPOL1_I9505PHNPOL1_PHN FW. - Search to download FW.

Nordic version of FW with PI1 modem "may" be used but I found network search for registering yields less number of networks. I have not tried using the Nordic FW.

2. Root the device using CF-Auto-Root.

3. Search for "Volte fix.zip" and download. Easiest way to get links to download is YouTube. In the zip file I used all files have 07-11-2016 as creation date. I found VoLTEFiles zip too with the same dates but did not try it so far.

4. Watch the YouTube, say, at "watch?v=MlkaziK6AkY" or any other relevant VoLTE zip file installation video to get the gist of the method before attempting.

5. The zip contains an Apks folder and a Files folder. Extract APK, csc folder, CSCVersion.txt and SW_Confgiuration.xml to a known folder preferably in ext-sd if available.

6. Install root explorer. It is under extracted Apks folder. Allow for installation of app from unknown sources.

7. Open Root Explorer browse to /system directory. Rename existing csc folder, CscVersion.txt and SW_Configuration.xml with some leading characters as fall back. The csc folder and the files can optionally be deleted as well.

Root Explorer will require the patition to be mounted as RW saying it is Read Only. Say OK to proceed.

8. Copy and paste the above folder and files obtained from zip to /system.

9. Change permissions via Root Explorer as below:

Touch the folder or file under Root Explorer. Once selected touch 3 dots on top right and select permissions. Given numbers can be directly entered using Octal button.

csc folder - 755 octal

CscVersion.txt - 644 octal

SW_Configuration.xml - 644 octal

10. Exit Root Explorer and Reboot. And wait patiently for a while until the two way sign appears on status bar. It really takes a while.

Call Settings - "Outgoing voice call settings" automatically shows "Use VoLTE when available".

Factory reset does not restore VoLTE icon on status bar and calling is not possible as well. Wait for a while for the phone to complete all processes after setting up. Reboot to get VoLTE back.

It seems to take a while and the Sammy phone will show a report being sent when connected to WiFi... to inform you later when you select "Software Update" that the phone has modified in an un-authorized way, etc.

Calling and messaging works even with WiFi ON.

I have not provided any link as the credit should go where it belongs.

See screenshots in the attached thumbnails.

ODIN Version used 3.12.7

CF-Auto-Root available on this forum.

And most importantly thanks to the developer who created the VoLTE fix files. And a special thanks to [MENTION=2875964]dhiru1602[/MENTION] with his PI1-VOLTE-JIO ROM as it was instrumental in making me search and test.