Skype is great for calls home. It costs a few cents a minute to call a land line phone number (you can call other Skype enabled computers for free). One of the nice features with Skype is you dial the number as if you were dialing from within the states, you don't have to worry about international codes.
Facetime is free for calling from one Apple product to another Apple product. I'm not sure if they've added the ability to use it for more calls (haven't used it for several years).
I also like WiFi for email and facebook - which also lets you stay in touch. WiFi is widely available in most hotels (may have to go to the lobby to get a strong signal), bars, and restaurants. If all else fails, you can always go to a McDonald's or Starbucks - they all offer free WiFi.