It's located in setting under network then you click on roaming it is called international CDMA it has always been turned on my iPhone 4s and I'm not sure what it is and if I should turn it off I live in the us not internationally.
U dont know the answer to the question so face palm to u I was asking if it should be left on or turned off that is all.
Simple, On allows you to use your phone from outside the United States, Off will not allow you to use your phone from outside the United States.
If you aren't going anywhere with the phone, leaving it on or off will do nothing to your service. Its just another slider you can play with.
is this for real?
Really?!? /facepalm
A good reason to leave it off, might be if you lived in the USA near the Mexican or Canadian borders
Reportedly, people's phones will sometimes jump to a cell in the neighboring country, and get charged for international rates.