It's now possible to download the complete north island or south island topo maps for offline use on Windows Phone using the NZ Topo Map app...
http://www.windowsphone.com/s?appid=...4-cbed66736b36
A handy tip: Turn flight mode on when you're in the bush without a cell signal, you're battery will last a lot longer! You can still use GPS for tracking while flight mode is on if you have a Windows Phone or Android device (iPhone's unfortunately turn GPS off in flight mode).
Regarding offline maps and SD cards...
Unfortunately Microsoft is really restrictive on Windows Phone 8 regarding letting apps use the SD card - a real shame and annoyance! Luckily most people should be able to upgrade their devices to Windows Phone 8.1 soon which makes better use of the SD card. You can actually install apps directly to the SD card. Should make the offline maps more accessible to some people who don't have the spare space on the phone itself.
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