And just in case they have fixed it by the time you're reading this, here's a screenshot.
What a helpful page.
johnr: Try this page
If you have a 027 number on Vodafone NZ the settings may come thru corrupted
cranz: Thanks HiK1000716, I'll have a look in to it
The issue is occuring when you hit the page securely (i.e. https) which happens if you've logged in to My Vodafone recently.
In the mean time you could try logging out and using John's link again - that should work..
richms: Why don't vodafone fix that issue with the configuration or at least make it unavailable for ported numbers?
Slingshot manage to send config info to a ported 027 number via vodafone ok, so its obviously doable.
richms: Even if they cant fix it, they could put a note on the page that it doesnt work to stop people from trying and finding that it does not work.
michaelmurfy: It's sort of working with me: