willnz: Yes, but 026 numbers are still charged, even at a slightly lower rate. The general assumption is, or should be, that if you're calling a non-geographical number it will be a chargeable call. 083210 is a difficult one, as it's a "value-added service" number. Generally, if a telco provides a service on 08X (other than free phone), they won't charge for calls to it, but other carriers might.
The general rule of thumb is, if a number isn't local, isn't toll free, and you haven't been explicitly told that calls to that number are free, then you should either expect to be charged for the call, or you should confirm whether it is a chargeable call or not with your telco.
Maybe if you have read the NAD (I have since, but hadn't at the time). I do not believe it is unreasonable for an average user to assume that they are NOT going to pay land to mobile rates for checking their voicemail. I wouldnt have cared if it was say the price of a national toll call but the point is it wasn't disclosed. 028 is not a well known prefix, and users shouldn't have to make assumptions about the cost of such calls, especially when they know its not a mobile.
I would have assumed that if they didnt want to provide a free to call number then they would have just given a local number in each of the regions they have numbers in but it seems they actually want to make money off people checking their voicemail from another phone provider (Which i don't have a problem with, just be upfront about the fact it is gonna cost me mobile rates - which we all know in New Zealand are very high)