I just tried to buy something online from a US merchant with my Visa card issued in Israel and I got an e-mail back saying that they are not accepting Visa or Mastercard's issued outside of the US, only American Express. The reason is that, for US cards they can match the billing address to what you entered, giving them some indication of whether it is your card, for foreign cards they cannot. A lot of smaller merchants have been bitten by fraud so they have stopped accepting the cards. I happen to have an American issued Visa as well so I don't have such a problem.