I just returned from a trip to Saipan (Commonwealth of the Northern Mariana Islands, a U.S. Commonwealth but usually considered "outside" the U.S.).

T-mobile's website says you have to pay for data and texting in the CNMI but I noticed during my trip my phone connected to "Docomo Pacific" and I received a "Welcome to Guam" text. In reviewing this month's bills there was no additional charges for the data or texting I used while on island.