[Windows Phone 8 General] anubis23:
Hello everyone, anubis23 here. It's has been a long time since I've posted anything on xda-dev. So here is my contribution to the community that has been good to me since Windows Mobile 5.

Disclaimer: This method may brick your phone! Back up all data. I am not responsible if you break your phone. Use the steps below at your own discretion! Please be careful.

I've finally had success in de-branding my AT&T Lumia 640 LTE, so that i was able to de-brand it and flash the T-Mobile US ROM on it so i could benefit from having band 12. During the past couple of weeks I've tried numerous methods as to de-branding my phone but kept running into bad luck due to signature errors and other miss fortune. At the end of the process to find a way to de-brand my AT&T Lumia 640 LTE i unfortunately half bricked my phone, where it had the red screen. My initial attempt to repair the boot loader using the WDRT was where it ended for me, as the WDRT restarted my phone and as a result full bricked it :(. It currently suffers from the QHSUSB_BULK error which is due to the partition tables being erase and i currently do not have JTAG hard to recover it, so i had to buy a MetroPcs board and swapped it into my phone.

Simple Process, won't bore anyone with the research, trails and errors i encountered.

Below I attached an archive that has 3 cabs in it that needs to be deployed to the AT&T Lumia 640 (which has the dreaded DeviePlatformId; MSM8926.P6204_ATT.1.1 lock on it) that you need to deploy to your phone using the iutool posted by WojtasXda.

Information about my Set-UP:

1. My Phone and girlfriend's phone was SIM UNLOCK (shouldn't have anything to do with the unlocking process, but meh)

2. I had the stock and freshly installed AT&T ROM (Windows Phone 8.1 Update 2) loaded onto it, using WDRT. The ROM that was: RM1073_02177.00000.15184.36016_RETAIL_prod_signed_1004_022B79_ATT-US.ffu from the WDRT software.

3. The device was not developer unlocked.

4. WDRT installed, with necessary drivers.

5. Windows 10 PC, with standard build, and insider fast build 11099. (Both build worked)

Step By Step:

1. Download the attached archive and extract them to anywhere you want.
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2. Place the 3 extracted cabs in a folder on the root of your PC. (ex: C:\Lumia\)
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3. Download and install the tools that contain the iutool. Found HERE.
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4. Open a command prompt window, with administrative privilege.
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5. Change the command prompt working directory to the location of the iutool;
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cd C:\Program Files (x86)\Windows Phone Kits\8.1\Tools\bin\i386

6. Connect your phone to your PC, (this goes without saying, you should have the WDRT [Found here] installed that way the necessary drivers are already in stalled.)
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7. With you phone connected, executed the code below, in the already opened command prompt window;
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iutool.exe -p C:\Lumia -V

8. The phone cabs will be downloaded to your phone and then install. Your phone will then restart to apply the cabs, and then start up with the "migration" loading screen to complete the process.
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9. Congrats you have now over written the DevicePlatformID in your phone so that you can now de-brand your phone to any other Lumia 640 LTE ROM.
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a. To make sure that you have successfully applied the cabs and the DeicePlatformId has changed, follow these addition steps.
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b. Download Kaptaiin LumiaFlashTools, found here.
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c. Extract the archive to a folder and navigate to the WPID folder and run the "Start.bat" to initial the tool.
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d. Once the program has launched, click on the "Flash a Windows Phone image onto your phone" option.
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e. With your phone disconnected from the PC. Turn off your phone.
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f. Press the POWER BUTTON and hold down the VOLUME UP button till you see the lighting gear screen, and then connect your phone to the PC.
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g. Connect your phone to your PC, and go back to the Windows Phone Image Designer application. You should now see that the device is recognized as "Flash-able Devices: Nokia.MSM8926.P6204.1.1", which indicates that the process above has finished successfully.
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h. You can now proceed to de-brand your phone with another Lumia 640 LTE image using this same method, by selecting the ROM to flash in the Image Designer window and hitting flash button or by following the method below.
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10. You can follow Kaptaiin wonderful guide that he and others has put together.
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Note: If you ever decide to use the WDRT to re-flash your phone. You need to run the code below to change the product code of the phone. You have to change the product code of the phone to make sure that WDRT does not re-download and install the old ATT ROM, which would then undo what we just did.

thor2 -mode uefiflash -ffufile "Location of your downloaded ROM" -productcodeupdate "new product code" -skip_flash

This will change the product code of your phone from the AT&T product code, to the T-Mobile US Product Code.

Flashing the T-Mobile US ROM.

You do not have to do this if you do not want to de-brand with the T-Mobile ROM, you are free to use whatever ROM you choose. Be careful to do research on other roms, to check to see if it alters the DevicePlatformId parameter in a bad way, like ATT did.

10. Download the T-Mobile ROM [US Product Code: 059X0P7] using means you have chosen to use, NaviFirm or Nokia Data Package Manager.

Seems like the NaviFirm and Nokia Data Package servers are still down and it seems like it might not return, however Petulinek found an alternative to downloading the firmware. Please be cautious when downloading firmware from non original sources.

If you guys decide to use the TMO rom that i used, here are the checksum information from the file that i have, which was downloaded with the Nokia Data Package Manager a while back.

RM1073_02177.00000.15203.26115_RETAIL_prod_signed_1001_023F70_TMO-US.ffu
MD5 Checksum: E0140458F031A610A7E06A5E5134D838
SHA-1 Checksum: 3EC8ABB689F435232A1280164B5B8242F88E3139
SHA-256 Checksum: 1B2CD97BD0CABFEAED13E6EED99902D7CD419B8DEA48CA7F1FBCC50758273CEF

11. Installing the downloaded ROM using WDRT.
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a. Open a command prompt window with administrative privileges.
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b. Run the following command:

cd C:\Program Files (x86)\Microsoft Care Suite\Windows Device Recovery Tool

c. Connect your phone to your PC.
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d. Run the command to start flashing your phone:

thor2 -mode uefiflash -ffufile "Location of downloaded ROM"

e. Wait for the ROM to flash and you will have a green screen, this means that flashing process was successful.
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f. Now restart your phone by holding down the VOLUME DOWN button and POWER BUTTON or just the POWER BUTTON, till it vibrates.
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g. Let your phone go through the install process.
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h. Once your phone has finish booting up and setup process completed, it is RECOMMENDED that you run the follow code to prevent your phone from re-downloading the AT&T ROM, either by phone update or by using WDRT. If you do not run this command after flashing your phone with the new ROM, your phone will redownload and procceed to load the AT&T ROM again if you ever decide to use the WDRT to re-flash your phone.

The Command below will change the product code of your phone from the AT&T product code, to the T-Mobile US Product Code.

thor2 -mode uefiflash -ffufile "C:\Lumia\RM-1073\RM1073_02177.00000.15203.26115_RETAIL_prod_signed_1001_023F70_TMO-US.ffu" -productcodeupdate 059X0P7 -skip_flash

Notable Credits:

Kaptaiin

WojtasXda

XDA-Community

e-Pig

Donations are always appreciated but are NEVER required.

Thank you boysie37, pile0g00, ombreman for your donations.

Note: If i have violated any of the posting rules for xda, mods please PM me with the violation and i will gladly fix it.