Is it illegal to jailbreak an iPhone?

Wikipedia claims that the answer on this is unclear. :-\

Isn’t breaking out of jail always illegal?

I have had a habit of hacking my Cell phones. If they can do it and I own the phone.
Then it is my right to get it to be all it can be.
It is selfish and greedy for them to shut off or prevent certain functions.

It’s almost certainly a violation of the contract you signed with AT&T and Apple that entitles you to use the software in the first place.

I agree with cwilbur. Although it is probably not technically illegal, it is almost certainly consider a breach of contract. However, the penalty for such a breach of contract is something I know nothing about. Most likely, it will have consequences similar to those of hacking or modding a Wii. If the mod or hack is discovered, they can probably remotely deactivate your iPhone. At least, that’s what Nintendo keeps telling me they’ll do if they discover a modification in my Wii. Hope that helps.