Why do I have to Erase my iPhone to switch carriers

Here is the solution. Find your "repair ID" email (which also has serial # of the old phone) and take that and your problem phone into an Apple Store and simultaneously submit a BBB complaint. A technician at the store has an iPad in which he inputs these numbers and sees all "lock/unlock policies" and that the "policy" on the replacement phone is wrong, and then he does an "escalation". In about 36 hours the problem was resolved. Apple called and said that it's fixed and I need to erase/restore it again. And indeed it became "carrier lock - no SIM restrictions", and doesn't ask anymore to "pick a carrier" during setup. So the problem is in a database somewhere (Therefore it could be that you need to have a network connection on the phone, which I do, so keep that in mind.) At this point I have no idea which of the two actions got this resolved. But, in the past, BBB resolved identical issues with big box stores. Apparently, it enters companies through a different door and works through a different department.

Yes, there seem to be 2 distinct problems: (1) Need to erase iPhone to switch carrier, (2) restore from backup makes the cell service not work (I suspect, the backup somehow includes the old carrier selection).

Problem 1 really looks like an intentional feature - it inserts the carrier selection dialog on the first boot and there is no way to proceed around it - that's what the other poster complained about. He apparently didn't yet realise the extent of the problem, because it was his first boot of the replacement phone.

Thank you for that article, I'll be able to try it the next time. This time I've already transferred my contacts and pictures from the previous installation, using SanDisk iXpand drive, and am manually reinstalling the apps, so I just don't want to start over.

[Edited by Moderator]