[Galaxy S 5 Q&A, Help & Troubleshooting] razes:
I'm struggling to activate VoLTE on my phone SM-G900T. Phone is unlocked and rooted with Magisk. Secret Code Explorer is installed.

Firmware T-mobile US. AP: G900TUVU1GQC2; CP: G900TUVU1GQC2. Android OS 6.0.1 (kltemo)

Baseband: G900TUVU1GQC2

Kernel: 3.4.0 Boeffla-Kernel-2.4-Samsung-g900f

Build Number: MMB29M.G900TUVU1GQC2

There is no Volte toggle in the Mobile network setting. However, the hardware supports ims and volte. And the Volte toogle is on in ImsService switch.

Here is Ims profile List:

T-mobile Volte/RCS ON

T-mobile Jansky LTE/wifi off

T-mobile Jansky 3G off

T-mobile E911 ON

Ims Info:

Ims Registration False

Voice over IP False

SMS over IP false

No profiles are registered

I have no idea how to register the Ims.

When I choose Main Activity in Ims Settings I get notification "no found CSC binaries or customer.xml"

Surprisingly, the DeviceKeystring Version Receiver (1234 code) shows only AP and CP are installed (G900TUVU1GQC2). But there is no CSC (modem). May be I have to flash CSC from T-mobile. I do have CSC_TMB_G900TTMB1GQC2_CL7500527_QB13003489_REV00_user_low_ship_MULTI_CERT.tar. I believe it from 2017.

I also have edited 2 config files. The first one is build.prop in System. The following lines were replaced:

ro.telephony.default_network=10 it was 9

persist.radio.sib16_support=1 it was 0

I also added the following lines:

# Debug Options

persist.ims.volte=true

persist.dbg.ims_volte_enable=1

persist.dbg.volte_avail_ovr=1

persist.dbg.vt_avail_ovr=1

persist.dbg.wfc_avail_ovr=1

# Radio Options

persist.radio.rat_on=combine

persist.radio.data_ltd_sys_ind=1

persist.radio.data_con_rprt=1

persist.radio.calls.on.ims=1

There is also option to add line

persist.volte_enabled_by_hw=1

meaning volte is force enabled using hardware instead of software

I didn't tried yet that opption

The second file I've edited is ims_nv_TMB.xml from /efs/sec_efs

<omadm LVC_ENABLED="1" EAB_SETTING="1"

VOLTE_ENABLED="1"

sms_over_ip_network_indication="1"

There is another file ims_nv_DEFAULT.xml in /efs/sec_efs that I didn't change

<?xml version="1.0" encoding="UTF-8"?>

<NV_STORAGE>

<omadm/>

</NV_STORAGE>

In addition I have added the ims to the APN type:

Mobile Networks:

APN: T-Mobile US LTE

APN type: default,mms,supl,ims

APN protocol: IPv4/IPv6

APN roaming protocol: IPv4/IPv6

Right now I able to make a calls and to send SMS but unable to receive calls and SMS. In Mobile Network Setting LTE/3G/2G Autoconnect is choosen (there is no LTE only option). When I making a call the network from LTE dropps to 3G (HSDPA) automatically. I can see it in the About Device/Status. Then most of time 3G is unavail (the 3G icon is x-crossed in toolbar). I able to restore temporarilly the 3G (HSDPA) if I turn off/on the Airplain mode toggle or if I restart the device.

I can choose LTE only option in Service mode RIL (2263 secret code). However, after that I unable neither to make or receive the calls.

So, I'm frustrated. I know people were able to activate Volte on Galaxy S5 even in 2014-2015 by upgrading with NF6 (baseband G900TUVU1BNF6). But nowdays I don't know where to get that update and would it will work with Marshmallow 6.0.1.

I would be grateful if someone who has experience with Volte activation on T-mobile US network will share his/her knowledge.