IRD only had a selection of toll free lines (High net wealth individuals, Kiwisaver, child support, info express and one more I can't remember) available for cellphone originated calls previously.
Since some point of time unknown to myself, they have opened up at least 5 more lines to accept calls from mobile phones.
0800 377 774
0800 775 247
0800 443 553
0800 257 843
0800 377 772
0800 377 776
I know that previously you could just dial any of the selection of toll free lines in the first sentence then say what you are after instead to bypass restrictions. But those without this knowledge can also ring 0800 from cell phones without paying for calls/ using minutes.
My personal opinion is that this is unwise. People tend to be quite ignorant and even those with unlimited calling minutes just dial 0800 numbers because they are just too lazy/can't be stuffed because it doesn't cost them money either way.
But in the end, any extra cost incurred by IRD or any government departments indirectly affect every New Zealander, so if you have an unlimited calling plan please refrain from using 0800 numbers when calling government departments.