Speaking of traveling, this article was very interesting on calling internationally for cheap.
We use SkypeIn and SkypeOut and have been very pleased with the service. With SkypeIn, we get a US phone number that rings our computer. This is mainly so the grandparents and great-grandparents can call us without needing any technical assistance. It is also really great because we can leave a US number with our US contacts like credit cards that we still have.
We do close down our computer at night though so that people who forget about the time change, don't wake us up!
I didn't know about the others he mentioned though but if you have used them successfully (or any other service), please let us know in the comments below!