Hey. Just to add my $.02, there seem to be a lot of companies on the web that will unlock phones. I've never tried any of them, though, but at least they may be a good option for you since Cingular doesn't seem so helpful.
As for the upgrade to international service, that's cool. If you think you'll travel outside the US even one more time, you should get an international sim. There are a few in the market, but they generally offer free incoming calls in a variety of countries and service worldwide (so you get the same number). Plus, they are prepaid, pretty cheap (esp. when compared to international roaming), and tend to last indefinitely. Outgoing calls aren't so expensive (they would probably be cheaper than calling cards, but make sure you check out the rates beforehand). Good luck, and happy travels!
Khalisha
Zengo Wireless