Business sales might be the best folks to talk to. It's only available on particular plans so may not be available on current in market plans.
If it were me I would try 0800 888 399 but if they don't know about local number on mobile then don't make any changes. Then next step would be to go to main local store with a business focus, e.g. queen Street, lambton quay etc. and talk to a business specialist there if possible.