SKYPE! or something there abouts.
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When traveling abroad set up a skype account, or something thereabouts (I am not actually advertising skype, I just use that as a verb to refer to internet calling)
Then from your Iphone or Ipad or similar wifi internet device (find a starbucks or a macdonalds, they are everywhere in the world) you can internet call for a few pennies.
However, getting a cellphone locally is certainly a more robust and better plan, as long as you aren't country hopping. I haven't found a good solution for that yet...