Hi John, whilst my colleagues are correct, the subject of locked iPad's is not quite so simple over here in the UK where you and I both are.
Unlike our friends across the pond, we do have the opportunity to purchase carrier locked iPads at significant discounts with an associated 12 - 24 month data contract. I'm assuming you have one of those deals with Vodafone. I myself had one with my iPad1 with Orange.
The short answer is you normally won't get it unlocked until the full contract has been completed, but to progress it you would talk to the carrier, in your case Vodafone. Apple won't have the slightest interest if you approach them directly.
But I'm certain if you have any number of months outstanding on the original contract they simply won't entertain it. Orange certainly didn't with me! But it can't hurt to try
Hope that helps.