If International roaming isn't on, it still connects to the service and then gives you an error
(in a language you probably don't speak) if you try to call anyone. This happened to
me once when AT&T "accidentally" turned off my international plan (while "accidentally"
continuing to charge me for it). This is definitely different behavior.
I've been putting off calling AT&T because of how painful it is, but maybe I have no choice.