I use AT&T and have the 120mb international data plan for $30. I've found that you can use Skype out to make calls using the local 3G networks. I've called locally for transportation and even called back to the states just to see if it worked and it does. Can't say exactly what the data usage is for these calls but not much, I've never come close to 120mb, and it's just a couple of cents/minute on the Skype bill.
Also I have the AT&T app and you can add or remove these features (I also have the 50 text message/$10 plan) very easily if you are or aren't flying an international trip