You're correct, except that it is "unlocking" that allows you to use an AT&T iPhone on another carrier. "Jailbreaking" is completely different - it simply allow

You're correct, except that it is "unlocking" that allows you to use an AT&T iPhone on another carrier. "Jailbreaking" is completely different - it simply allows you to install unsigned software. One must jailbreak their iPhone before it can be unlocked, because you need to run special, unsigned software to unlock it.