Unless their help and support website is very wrong it looks like Megatel now support landline via both ONT and their routers.

Nova's website offers a static IP address for $10 a month. That should be an opt-out route for CGNAT.

https://support.2talk.co.nz/do-i-use-pppoe-or-dhcp

2Talk supports both. 

https://contact.co.nz/personal/broadband/modems

"Fibre with VoIP phone 
A Contact modem is required (you can’t bring your own). "

Contact supports voice but only through their supplied router. 

Genesis requires VLAN tagging.

CGNAT is used and $10 / month static IP required for a public IPv4 IP.

https://www.genesisenergy.co.nz/broadband/help/faqs

One part of the FAQ says they support both IPoE (DHCP) and "PPoE" while another says they require IPoE. 

2talk also supports voice via ATA as they don't require a broadband connection with them to have a voice account.

https://support.2talk.co.nz/what-do-i-need-to-use-2talk-voice

Voyager also supports voice via ATA

https://www.geekzone.co.nz/forums.asp?forumid=190&topicid=306921