I only ask because I was watching one of the UK news programmes last night and some drooling idiot of an economic commentator said "We've all had the experience of using our Mastercard to pay off our Visa" and Sam and I wondered how that works since we've never been insane or desperate enough to try to do that.
Or if you're really dumb and desperate you can use a cash advance at an exorbitant interest rate from one card to get cash to pay the other one. We have met the enemy, and he is us — Pogo