UPDATE UPDATE: Tried again to create Amazon Account but again failed at the telephone number stage.
However, I went direct to the US Amazon Prime web site and proceeded to set up Account there, and this time only got the TXT One-Time Password window, and then the option to enter credit card details.
At this stage I exited the web site, and then went to the NZ Amazon Prime reference site, logged in, and then entered credit card details when offered Video Sign Up.
Obtained Code off Vodafone TV device, registered it on the web site, and et voila we have Amazon prime Video 😊😊
Not sure if the 7-days free will be recognised, but the site did state this on the VTV Code page.