I guess most of the new phones are qorld-wide (quad-band). In the old days, even having a tri-band ohone was not enough to get coverage in non-USVI (Puerto Rico and St Thomas) islands.
But the newest phones do have coverage, it seems. I will wager it is still $2.50/minute on up. And if you are receiving data (email) it can get VERY expensive.
For my iPhone, AT&T warned me to turn off data-roaming while overseas, or it could cost me hundreds of dollars on my next bill.