[Google Pixel 2 Guides, News, & Discussion] darkhole:
It worked for my using Pixel 2 Walleye with Android March 2020 installation, i'm going to detail more this procedure, because it's hard to do it from scratch.

I also used information/files from here: https://xdaforums.com/pixel-2-xl/how-to/guide-qxdm-port-activation-pixel-2-xl-t3884967

Steps with links

0. Remove any fingerprint/pin/lock pattern from your phone and keep it that way until the end. ALSO, UNLOCKING THE BOOTLOADER WILL WIPE ALL YOUR DEVICE (apps, photos, files, accounts) BE CAREFUL AND DO A BACKUP

1. Find the QPST installer (only available for Windows) (seems to be an internal Qualcomm software), I used version 2.7.474 from here https://qpsttool.com/qpst-tool-v2-7-474 . Save it and install it in your Windows machine.

2. Install adb tools Windows, macOS, Linux: https://www.xda-developers.com/install-adb-windows-macos-linux/

3. Enter Developer Mode in your Pixel: https://developer.android.com/studio/debug/dev-options#enable

4. Unlock bootloader of Pixel 2 (this one is easy BUT IT WILL WIPE YOUR DEVICE), connect your phone to your PC (you may need to wait a few minutes for the automatic installation of drivers) and follow the procedure (you may need to run this as an Administrator) https://www.xda-developers.com/how-to-unlock-bootloader-and-root-the-google-pixel-2-and-pixel-2-xl/

5. Fastboot boot twrp img for temporary twrp: https://aubykhan.wordpress.com/2013...t-into-twrp-or-cwm-recovery-without-flashing/

6. Install twrp zip from twrp recovery for permanent twrp. I installed TWRP (TWRP is a recovery replacement of the official recovery inside Android phones) https://www.xda-developers.com/how-to-install-twrp/ TWRP will help you to install Magisk

7. Flash Magisk-v19.0_Taimen_Diag.zip from twrp: You have to download the file from first post https://xdaforums.com/attachment.php?attachmentid=4742296&d=1555223123 and save it in your Phone. And then open TWRP (go to recovery mode https://www.hardreset.info/devices/google/google-pixel-2/recovery-mode/ ), then you have select the install grey button in TWRP and find your Magisk file and install it, you will need to reboot your phone. Magisk is a tool that helps to modify Android behavior without root access, old times ago having root was not an issue, but right now because of security and restrictions (Netflix, DRM, etc) it's better to not root your phone. Magisk will help you to made modifications without touching too many things in your phone.

8. Install drivers inside Windows to recognize your phone (these are special drivers, as your phone will be recognized as a Serial device for QPST) I used this for Window: https://mega.nz/#!oMEHTIbA!0g7ahr8r81Q3ue8LpEy-sfd7FTLEEQlGRi2CJfG_Kq0

9. Download to your Android the file app-debug.apk https://xdaforums.com/attachment.php?attachmentid=4742298&d=1555223123, this is the Magisk App to manage Magisk from Android. Open it to install the App.

10. Download Pixel 2 Diag Port.zip file to your phone from here https://xdaforums.com/attachment.php?attachmentid=4677339&d=1546269352 and VoEnabler to your Phone from here https://xdaforums.com/attachment.php?attachmentid=4788885&d=1562579515 (this is for Pixel 2, you may need to change the VoEnabler for other Pixels, or it may work, who knows)

11. Open the Magisk App (installed in step 9) go to Modules section, add with the yellow button at the bottom the Modules that you downloaded in the step 10, Pixel2DiagPort and VoEnabler. This will allow you yo use a setting under Settings -> Network & internet -> Mobile network -> VoLTE.

12. Download the mbn file from here inside Windows https://xdaforums.com/attachment.php?attachmentid=4691778&d=1548185827, unzip it and search for your region and your Mobile Network Operator . Android OS is split in multiple parts, the mbn have the Mobile Network operator information needed. All this procedure is to change this file!

13. Connect the phone to your Windows PC, now open QPST tool in Windows (the name is Advanced PDC Tool and the icon is orange and grey), fingers crossed!, in the dropdown called Device you will see a Device Qualcomm... serial... choose it. Then press the button Load and select the .mbn file for your Operator (Step 13). This will allow you a new option in the list of the Advanced PDC Tool. You have to be careful and look for the one that you just added. Right-click on new loaded profile and select SetSelectedConfig - Sub0 then press Activate.

14. Restart device and check if VoLTE is working! You may need to enable it in the preferences Settings -> Network & internet -> Mobile network -> VoLTE

If you need more detail please let me know.