Just submitted to Sony ... probably won't make a difference, but worth a punt:
"Hi - I'm a New Zealand Vodafone customer. Just a quick bit of feedback - it would be great if the 2018 Xperia range could be made available to the Vodafone network in New Zealand. Recent Xperia releases have been exclusive to the Spark network in New Zealand which means Vodafone customers miss out on being able to purchase Xperia phones on their Vodafone contract (and Sony misses out as well). I'd like to upgrade to a new Sony this year, please make your upcoming Xperia range available to the Vodafone New Zealand network."
And Vodafone NZ - if you could hold your hand up to Sony for the 2018 Xperia range, that would be great!