I carry with me a prepaid calling card you can pick up at Sam's Club or Costco. The rates are 3-4 cents per minute and there is a payphone surcharge of about 75 cents. You dial the toll-free access number and use the pin on the card. Much less than the credit card rates. Although I have not used them from outside the US and do not know the rates, there is also a list of access numbers for many countries.
Also very handy for making calls from hotel rooms.