I was on the kiwibank visa debit website here:
http://www.kiwibank.co.nz/visa-debit-card/faq.asp
And on the question of "why do some services that accept visa not accept visa debit cards?" it says vodafone live may not accept visa debit cards.
Anyone confirm if vodafone live accepts visa debit cards?
Most new zealand banks offer debit cards now(asb,westpac,kiwibank etc) partly because of the recession is meaning debit cards are more popular than credit cards because the money is deducted from your bank account so you don't pay interest, so i'm guessing alot of over 18 year olds would be getting these now, so you'd hope vodafone accepts visa debit cards to verify a person's age for the r18 vodafone live services. If they don't, then they should. Just do what adult websites do, have a disclaimer saying "you confirm your 18 or older, continue or exit".