AT&T Nokia Lumia 920 Firmware Switching

Update 2021-05-01: The link died. I need to submit the archive to the Internet Archive.

On the AT&T Nokia Lumia 920, AT&T has made it pretty nearly impossible to switch firmware to a different variant. In my case, I don't have AT&T in the first place (I'm with T-Mobile), so having features locked out because they felt like it is really unhelpful.

To flash a firmware on the AT&T Lumia 920 (RM-820), which you can download with NaviFirm+ or another utility, you must first acquire the pre-Portico Rogers Windows Phone 8 firmware. It is handily available here, but if that link dies, I have a copy. Each of those files is prepended with a checksum; remove the checksum from the filenames.

Flash this firmware. I did nothing special - it worked as you'd expect. My phone thinks it's Canadian. Go through the setup process, but don't bother syncing anything down yet. Once the phone is up, get network connectivity working and then go to Phone Update and update the phone. This will get you to Portico. Note you can't actually flash Portico yourself, because the bootloader or something won't let you.

Once updated to Portico, reset your phone. Settings, About, Reset Your Phone. This will help ensure that nothing fishy happens.

Once that's complete, you can flash your firmware choice. I'm going with the EU Dev Phone (product code 059R4H6, model number RM-821). If this ends up losing LTE for me, I'll probably flash to a Latin America RM-820 country variant (CV). You should be able to flash any version on top of any other version now, except you won't be able to go back to AT&T versions.