Yes, sorry about that, should have mentioned where they will both be visible...as per the article:

...there will be just four locations in the whole country where customers will see the One and Vodafone logos side-by-side: the international airports at Auckland, Wellington, Christchurch and Dunedin.

“Probably the biggest risk for the change is people getting off planes and going ‘I don’t know One, I don’t know 2degrees and I don’t know Spark, but I do know Vodafone’. So at the airport you’ve got them co-branded side by side. That’s the only place where the brand will officially survive in New Zealand.”