(I had actually posted this question earlier in the wrong sub-forum, and if a mod doesn't delete it from there, then I'll do so myself later on).

(For the following questions, assume that the phone is question has been activated once originally).

If a CDMA iPhone 5 (Sprint or Verizon) with a bad ESN is given a firmware upgrade/restore, during the setup process that comes up afterwards (in which we specify the region, set up iCloud, etc), can Apple block the phone from reaching the home screen? That is, does Apple have a database of blacklisted ESNs by which it can lock down phones during the setup process and prevent them from reaching the home screen? Or can the carrier do so? (The latter won't be a problem, since I plan to use the phone abroad, unless this check is carried out with the carrier's servers over wifi).

As long as I can reach the home screen, that's fine, since one can always use a hardware unlock feature from there. But if Apple prevents this, then of course it would mean that I can never upgrade the firmware.

Also, is it sufficient to simply use any non-functional Sprint or Verizon SIM card to activate the phone during the setup process, or does it need the original SIM?