nztim:

 

JPT:

 

I think buying a ATA (or IP Phone) and configuring it as described at the beginning (switching to TCP instead of UDP), sounds like the most sensible fix. Good to have arrived here with all your  help. Cheers.

 

 

Personally I would change the SIM to Spark, use direct.telecom.co.nz as your APN, your CGNAT will disappear, and you wont have any of the issues you are experiencing, it will just work

 

Thanks, good to know. Will look into that too.