Another option is to use a Skype Phone. The tradeoff is that you have to be at your PC because it is VoIP. I use it to talk to friends of mine in Brazil and Chile. Excellent quality.

http://www.skype.com

Completely free when making Skype to Skype calls (both people have downloaded the free software). Skype makes money by charging for Skype In and Skype Out minutes. Skype In means people can call your cell phone for example (i.e. you have a New York cell phone that anyone can call) and the calls gets routed to your Skype phone no matter what country you are in. Skype Out means you can call any landline in the world for a fee. I highly recommend buying a headset or skype phone because the quality is excellent (much better than your PC's built in mic and stereo). I use the Motorola 500 Blue Tooth Earpiece. Rocks. I bought the CIT 200 from Linksys, but had an issue with the battery.

I love skype. Talked to my buddy in South Korea yesterday. Perfect! They were bought by eBay for like $2.2 billion.