I've just had two customers within five minutes who can't resolve www.bnz.co.nz - They can resolve bnz.co.nz but not with www on the front. We changed their DNS to google (220.127.116.11) and they can then resolve it fine.
Interestingly www.bnz.co.nz resolves to xoqza.x.incapdns.net who run a service to block bad bots etc from resolving DNS to stop them getting to your website which may or may not be related (Perhaps Vodafone's DNS servers are being blocked by the Incapsula service??).
Either way it appears Vodafone are having DNS issues. At this point they don't list any faults and neither do BNZ but if you have issues with BNZ (or clients accessing it) this is likely why so see if they/you use Vodafone as a provider first.