The NZ phone services used to be a bit of a nightmare with phone numbers being anywhere from 1 to 6 digits, and STD (subscriber toll dialling) code from 1 to 4 digits.
This all changed in the 90's to a regional standard plan, one digit toll access, one digit area code and 7 digit phone number.
A = Toll access code
B = Wellington
C = Tryphena - Benneydale
D = Porirua + Upper Hutt
E = Masterton
F = Glen Murray
Use last digit of any longer numbers
Cache at S41 06.ABC E174 52.DEF
Check sum = 29
Cache is a small container with a log only - BYOP
For reassurance, you can check your solution here with Geocheck.org