I gotta let you in on this one guys :-) Before Google voice I used to buy crappy callback cards, or even expensive "kalam" cards, or skype to a GPRS connection... (with a 8 second roundtrip), or intimate midnight conversations with the phone operators on 100 (maybe the least useful job in the world)...
Now I installed Google Voice, and I call from right within gmail, and I'm speaking to an Italian mobile number, for 2 cents a minute! The voice quality is great, it's stable, and doesn't require the other party to have any internet connectivity and/or software installed.
The cost kinda surprises me, because the rates on this page:
https://www.google.com/voice/rates
say that Italian mobile phones cost about 20 cents a minute, and the land lines are 2 cents a minute... I'm not gonna complain though! Yeah some country stay expensive, like Dubai... but overall I think it's the best way to place international calls (AFAIK) especially towards developed countries.