Apart from AT&T, is there a carrier (anywhere in the world) that updated the 640 line to W10M and still support the device?
Nobody is supporting the 640 specifically now. Microsoft isn't putting out updated firmwares for it so there's nothing for carriers to specifically approve.
MS is putting out the usual W10M updates but they don't need carrier approval.
So everyone with a Lumia 640 needs to be a Windows Insider to get it?
Ah I might've been too ambiguous, I meant that the 640 is still supported by Microsoft across the board for the general Windows 10 Mobile releases independent of the carrier. Under Windows 10 Mobile's update system, carriers can block/inspect firmware upgrades but in this case, there are no firmware upgrades for the 640 to be had in the first place which is what I meant.
(I am assuming that all 640's were cleared to use the Windows 10 Mobile upgrade in the first place)
Oh oh I understand. No I'm was the one who was too vague. I'd like to put my 640 on a ROM from a carrier that released the W10M update so I can get it without enrolling in the insider program. Is there such a carrier (to your knowledge)?
Is there a reason you can't go with an unbranded (CV) ROM?