If you are interested in practicing medicine outside of the country on a permanent basis then it is as OzDDS says. However, if you are interested in practicing medicine in poor and under-served countries on a temporary basis, as I am, then you will have no problem at all in most countries. You can even join doctors without borders as a DO.
VCOM has an international medicine program that does missions to some countries, expenses paid if I remember correctly, and also has a very nice plan for residency. If you commit one year to their international medicine program during residency they will forgive a significant amount of your loans. The more years you commit the more they forgive. NSU also does international medicine missions, to Guatemala and Peru I believe, but the expenses are your own there. This was part of what I took into account when choosing my school and although UMDNJ doesn't have a program like these other schools, it does support students going out of country for elective rotations and the school is very supportive of student interest and clubs. I plan to look into starting an international medicine club, along with some of my classmates, which will hopefully hold yearly missions to places like Honduras and India. The point is, if you are interested in international medicine to serve the underserved communities in the world then you can make it happen but choose your school wisely.
Good Luck