Nokia New Zealand and Telecom acknowledges the Lumia 800 compass is faulty.
Nokia New Zealand and Telecom NZ will NOT guarantee the Lumia 920 compass is free from the same defect affecting the 800.
So there you have it. Buyer beware I suppose. This actually sets an interesting precedent as it means Nokia and Telecom will openly sell you a Lumia 920, listing the compass as a feature, but will not guarantee that it will perform accurately. I guess the only argument Telecom could make is that it has a compass (it just points the wrong way).
If you're stuck with a Windows Phone with a faulty compass, unfortunately neither Nokia or Telecom can provide you with a device with a working compass - as they won't guarantee any of their compasses work.
So my advice to everyone who has a Windows Phone with a faulty compass - return it immediately for a full refund of your purchase price. If like me you received it free on contract, then unfortunately Telecom won't give you a refund or let you exchange it. Your best hope is that they allow you to cancel your contract, but this is extremely rare.