Can you buy calling cards so you can call U.S. from England and Scotland?

[D L and K's Mom]

I am not a world traveler....IS there such a thing as a phone card that I can buy here in the U.S so DH and DD can call me from England and Scotland? I don't think the regular ATT cards you buy here in the U.S. will work will they? I was told No, by my MIL but I want another opinion. I figure she is right since you have to call a # before you place your call and the # is probably a US #. Our Verizon cell phones will not work. Some other cell phone carriers do but ours..NOPE! figures. I will probably post this on the UK board too. Thanks in advance. If you can buy them where do I buy them? Post Office? Travel agency?? thank you so much!