There was a carrier settings update that came through at the same time - perhaps that's the issue?
Someone on our Australian team who was over in NZ this week upgraded his iPhone to IOS 11 while he was in NZ and had problems where he couldn't receive calls. Probably because he missed the carrier update that came with it.
His phone has a Vodafone AU Sim. So it would be on Voda NZ when he was here. I would say there are some critical carrier settings they need to pull.
You can force a re-check for carrier settings by going to Settings>General>About and it'll run a check when you're in there.
Confirmed working on my mates iPhone with iOS 11 but have not tested on the flatmates handset yet as they will only upgrade when first update is out for iOS 11
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