[Addendum: The FCC does not endorse the VoIP services mentioned below or any distinct technology.]
We've gone over many different options for international calling which all revolved around use of wireless networks and landlines. However, there is another cheap and easy way to make international calls called Voice Over Internet Protocol (VoIP) through a Wi-Fi hotspot. This allows you to call someone using high-speed Internet service instead of a telephone service. Just make sure that your phone does not automatically connect to an international mobile network, which can be expensive to access.
Of course, you must have Internet access to use a VoIP service, as well as a computer with microphone or webcam, or a smartphone that has VoIP capabilities. Assuming you have access, you can use one of many popular VoIP services such as Skype, Fring, or Truphone. If you use a VoIP service to make a call to another person using VoIP, it will probably be absolutely free (not including any fees you may have to pay to access the Internet). If the person you are calling is not using VoIP on their computer, you can also call them directly on their phone. This is often cheaper than using a calling card or local SIM card.
The main advantage of using VoIP to make international calls is that it is very inexpensive (free in certain circumstances). The downside is that it requires Internet access, and a computer or mobile device that has the necessary VoIP application. Also, international equivalents of 911 and E911 may not be fully functional with VoIP calling. Make sure you are aware of these limitations before relying on VoIP as your primary calling method. Visit the following links to learn more about VoIP services and to look up calling rates to individual countries.
UK +44 (0) 203 318 0742
USA and rest of world +1 (646) 360-1689
As always, check out our tip sheet, Wireless World Travel Made Simple, for detailed tips and provider contact info.