I don't know; when I get calls that are hangups, I tend to consider myself lucky and forget about it. After all, a fair number of us realize we're dialing the wrong number and hang up fairly innocently.

Now, if someone kept calling and hanging up I'd be annoyed. If it was just the once, maybe you won't hear from them again. Besides, I interrupt the patter with, "Sorry I'm not interested" and hang up. No point wasting their time or mine.