[llkashll]

Question for anyone who's been able to try it (unfortunately... or perhaps fortunately all my phones are carrier unlocked).

I'd assume that upgrading from Win 8.1 -> Win 10 would preserve any carrier locks, but assuming locks are enforced at the OS level, a revert from Win 10 -> Win 8.1 should wipe any carrier specific information (since the revert process uses a stock build and doesn't retain any configuration).

Anyone given it a shot? Has it worked? Apologies if this has already been asked, I could only find information from the Lumia 920 days prior to the insider program and recovery tool.

[ashram]

my 920 and a friend's 1520, both at&t variants, have remained unlocked after upgrading (or using the restore tool)

Going insider will not automatically unlock you phone, but if you unlocked it already, going insider should not change that fact at all.

[MP3Mike]

I'd assume that upgrading from Win 8.1 -> Win 10 would preserve any carrier locks, but assuming locks are enforced at the OS level, a revert from Win 10 -> Win 8.1 should wipe any carrier specific information (since the revert process uses a stock build and doesn't retain any configuration).

The WDRT process downloads an image that is specific for your phone. So it comes with all the carrier bloatware, if any, and all. I have a 640 that was carrier locked on WP8.1, carrier locked when upgraded to W10M, still carrier locked when restored to WP8.1. I got the unlock code from T-Mobile and now it is unlocked with either WP8.1 or W10M. I think the carrier locking is maintained in the hardware, not in the OS/firmware.

[lexrsk]

Carrier locking is via the IMEI number therefore regardless of the firmware or OS version it will remain locked.

[llkashll]

Thanks guys, really much appreciated, just saved me a couple of hundred picking up a phone and being disappointed after it didn't work. Hope you all had a Merry Christmas and a good new year coming up.