I always just buy a local phone card. You get a pretty fair amount of talktime -- that's assuming you are just going to call the U.S. for brief chats and not an hour-long conversation. The cards have an access number, in English, and you just scrtach off the card to reveal the calling card number. You get a balance before the start of each call letting you know your remaining balance and associated talk time.
One note, not all calling cards work at all public phones -- I was at one of the malls either Ibn Batutta or Emirates and the Etisalat card would not work -- was told a different card was required. Worked fine from the hotel though.