Not sure on voice alerts (my GPS was too old) But I use to maintain my own POI warnings for redlight/speed camera. It was exported from a features database (zenbu) and converted/imported. You got tones when near and a different one for exceeding a specified speed. I think similar works for the voice ones.

It doesn't help however when people decide to load said POI and get annoyed with the warning zones so decide to self-edit the wiki and remove them!!! (hence the shift to my own). Youll see a few do it. Theres a POI download link and some info further back in history how to DIY

http://gwprojects.org/forum/viewtopic.php?f=4&t=1187&start=180 

Thank you

I was wondering if there is a file already in existence either commercial or custom

last page of that has a NZ specific one one of the users released.

Rt cick save as, dump into the POI folder on the storage and the rest is automatic. It'll need updating soon as wellington expands their collection and then nationwide.

And if you feel your maps are out of date they also have a alternate NZ map set to use. However you lose the speed indicators and searching process needs to change. 

Hi

Last page seems to be 14 and no files there.

 13.

http://gwprojects.org/forum/viewtopic.php?f=4&t=1187&start=180#p33618

Link is included as part of his text 

Routes to.. http://www.nzopengps.org/public/POI_Files/Fixed%20Cameras%2020141023.gpi 

But as you see it may not be the most up to date. Community driven afterall