Payment methods

[Faragon]

Never mind, found an answer :)

If you log in to your account page on the WoW website, there's an option to "Add Game Card". Just click that button, enter the game card's code, and the game card will be added to your subscription after your current payment period. The page shows a list of all of the payment periods (including recurring credit card payments, game cards, free days, etc), that you've used and that are coming up, so it's all easy to keep track of. If you want them to stop billing your credit card, you can cancel the recurring subscription from that page, as well (or switch to a different card if you ever get your own CC later on).

So in short, yes, you can easily switch to game cards after paying with a credit card for a month.