Interesting that it's the first six numbers and not the last six numbers. Since the first few numbers of the card are typically similar or the same for a particular issuer, a quick Google image search got me 6 numbers that work just fine. From the Visa Signature promo (and these T&C's), I know you won't get the bonus points without actually using a Visa Infinite card, but if you need gold for next year, this might be a good way to get it.