As we know, Redmi Note 4X (Snapdragon 625) actually supports three major Chinese carriers, China Mobile (CMCC), China Telecom(CT), and China Unicom(CU) VoLTE and Video Calling, but only CMCC is enabled in carrier config of MIUI offical ROM.Therefore, I would like to share how to unlock VoLTE for CT and CU without root. First, it’s necessary to update Redmi Note 4X with the latest version V11.0.2.0.NCFMIXM.

The following steps:

  1. Unlock Bootloader,But your device has not to root.

    Steps of detailing 👉 https://www.imobie.com/android-unlock/unlock-bootloader-on-xiaomi.htm

  2. Install TWRP Recovery

    Steps of detailing 👉 https://twrp.me/xiaomi/xiaomiredminote4.html

  3. Update the modem firmware with TWRP

    You can download the custom firmware HMNote4X_V11.0.2.0_volte_modem for Redmi Note 4X and copy to your device. By the way,under weak signal environments, the modem will not work any more.

  4. Reboot the device.

    The “HD” symbol on top of a phone screen typically indicates that the device is unlocked to VoLTE.

Reference:

  1. https://xdaforums.com/f/xiaomi-redmi-note-4-snapdragon-roms-kernels-re.6145/

  2. https://xiaomirom.com/en/rom/redmi-note-4-mido-global-fastboot-recovery-rom/

  3. https://pve-alist.lzyy.link/OneDrive/

  4. https://www.miscw.com/how-to-enable-volte-and-vowifi-on-xiaomi-smartphones-non-root-android-11-or-10-solved-41243.html