There is no NZ ISP that fully supports IPv6 on DSL/UFB that I am aware of.
Let's change that awareness then! :)
Very first question on their list: "Can I get IPv6?"
Answer: "I'm so glad you asked, yes all our plans are IPv6 enabled."
That statement makes me think they seem pretty supportive.
*disclaimer - I am not a customer of Sinch, nor have I ever used their products. I simply had their service pointed out to me recently, and I think I maybe I'll get a test circuit from them sometime next year.
Pete