Correct. Well, you cannot do it on a stock phone. The only way would be to jailbreak and install a tweak allowing this. I do not jailbreak, so I don't know if such a tweak exists. But that would be the only way.Right and from what I've heard only a jailbroken phone can do it.
Go to the jailbreak forum you'll find more helpful info than here. I know it's possible but don't know the name of the tweak.