[Windows 10 Mobile] nate0:
I could not find a thread to walk through being able to get my Dual Sim 950 to officially work on AT&T with VoLTE and other services (Enhanced LTE/HD Voice etc...). I searched many forums and threads to find a way to do this. I got tired of the lack of call quality and other quirks for my Lumia while on ATT. After accumulating several different pieces of information from multiple sources and places on the xda forum I was able to make it work. This is my first official post with the intention of it being a guide, offer tips if you want. Or if you see errors offer advice or suggestions if needed.

I am only posting this in the event someone else needs the information or wants to use it in some way. Messing with hidden partitions is risky and so if you brick your device using this thread, I'm sorry but I cannot help you. So if you choose to use these directions, use them at your own risk. I cannot be remote technical support. Thanks.

Here is how I got this to work.

Steps I used to convert NAM 950 DS RM-1118_13058 (059X5G2) to an ATT Lumia 950 (RM-1105_12716 059X4D9)

-1- First I flashed this specific original rom for my Dual Sim 950. I used the ffu located here.

-- thor2 -mode uefiflash -ffufile "RM1118_1078.0027.10586.13058.15358.030FF5_retail_ prod_signed.ffu"

-2- Second I manually pushed three cabs to my phone to alter the plat ID to Microsoft.MSM8992.P6218_ATT.1.0. All three were alone in the directory. Listed them below:

mmo.device_talkman_lte_americas.phone.plat_d20cefe ddb10fb6737b56fa966533783b1288e44.cab

mmo.base.variant.plat_55ce525fdf57ab0d614ada3517c3 4c84029f5437.cab

mmo.base.phone.plat_96ea6a2d24151eaf6299c342f81f49 997ca44137.cab

-- iutool.exe -v -p "C:\CABs\Your_Location-of-RM-1105_Plat-cabs"

-3- Third I did a full NVI flash and Reset with an ATT ROM. Link to location of ffu I used here.

FFU File used: RM1105_1078.0053.10586.13169.12716.035044_retail_ prod_signed.ffu

-- thor2 -mode uefiflash -ffufile "RM1105_1078.0053.10586.13169.12716.035044_retail_ prod_signed.ffu" -do_full_nvi_update -do_factory_reset

-4- Fourth I updated the product code. (Note: I never kept my phone on the ATT ROM long enough to see if this was really needed, but I suspected potentially an OTA update might revert it back to the Dual Sim variant.)

-- thor2 -mode uefiflash -ffufile RM1105_1078.0053.10586.13169.12716.035044_ret ail_prod_signed.ffu -productcodeupdate 059X4D9 -skip_flash

After it is finished while in this mode you can run thor2 -mode rnd -readdeviceinfo to check the device details also to verify the changes.

-5- Fifth I registered an imei of the att Lumia 950 I had to my ATT account to have ims registration complete.

Steps I used to convert back to NAM 950 DS RM-1118_13058 (059X5G2) from an ATT Lumia 950 (RM-1105_12716 059X4D9)

-1- First I flashed this specific ATT ROM. The one I used is located here.

-- thor2 -mode uefiflash -ffufile "RM1105_1078.0017.10586.13053.12716.02FBB4_retail_prod_signed.ffu"

-2- Second I manually pushed three cabs to my phone to alter the plat ID back to Microsoft.MSM8992.P6218.1.0. All three were alone in the directory. Listed them below:

mmo.base.phone.plat_8bab003dbd82a4acc5989f812a0dcd284eccfe43.cab

mmo.base.variant.plat_c7b2c481e64fe6a806f52df8f5f55c59fbb6a81e.cab

mmo.device_talkman_lte_row_dsds.phone.plat_d7303236cd88dda5a304701d5b59b0c2d5260d7c.cab

-- iutool.exe -v -p "C:\CABs\Your_Location-of-RM-1118_Plat-cabs"

-3- Third I did a full NVI flash and Reset with a NAM 950 DS ROM. Link to the ffu Iocation here.

FFU File used: RM1118_1078.0027.10586.13058.15358.030FF5_retail_prod_signed.ffu

-- thor2 -mode uefiflash -ffufile "RM1118_1078.0027.10586.13058.15358.030FF5_retail_prod_signed.ffu" -do_full_nvi_update -do_factory_reset

-4- Fourth I updated the product code back to the NAM Lumia 950 DS variant just in case.

-- thor2 -mode uefiflash -ffufile RM1118_1078.0027.10586.13058.15358.030FF5_retail_prod_signed.ffu" -productcodeupdate 059X5G2 -skip_flash

What helped immensely was being able to locate and find those cab files. They are added here for convenience. I found a thread posted here on the forums that helped a ton. Even if it was a cumulative effort, a thanks to [MENTION=269273]TristanLeBoss[/MENTION] for posting it.