If the device is provisioned for international roaming then absolutely it will work. You can make sure everything is set up correctly by chatting with our customer service.
Have a great and safe trip
Here is some advice. Don't use your US SIM for calls within the country where you are unless you are stinking rich. Even if you have international roaming and the discount, it will cost you a fortune. Unlock your phone. T-mobile will do it for you at no charge, They did it for me. If not, lots of people on eBay will send you the necessary code for a reasonable price, around $25 I think. And buy and use a local SIM.
For calls from back home, get a phone card or use Skype or google's phone service. With a phone card, I think you can pick up your voice mail and reply using Skype. I don't know what calls to the USA from the country you are in using a local SIM will cost you. I think google will hi-jack your calls to your own phone number if you configure it that way.
Yes, it is a bit more complicated than simply using your US SIM, but believe me, if you don't and use your phone for "local" calls in the country you are in (e.g. to your hotel, etc.), you will faint when you get your bill.