Never use your RL credit card with any agency. too dangerous because of unscrupulous employees having access to RL data now. Cash is of course preferred. But, if you are doing transactions over the phone, how can they get the cash? Obviously not. So go buy a pre-paid Visa/MC from the checkout stands at Wal-Mart, and pay cash for it to the checker. (btw- this is the same procedure when buying your hobby phone from a retailer. pay cash for it at the checkout. when you buy those 'minutes' cards, pay cash for them.)
I always carry a pre-paid visa card with me, that way if I go into questionable areas, I don't have a 'fat' wallet enticing folks who are looking for their next meal.