Is Jailbreaking an iPhone illegal?

If you are trying to just modify the operating system (Like changing the layouts, adding non illegal features, etc.) is not illegal.

However, if you are trying to cheat a game by getting in app purchases for free, that is illegal (Though most apps have protection to ensure they have received the money before giving the purchase), or trying to get apps for free; that is illegal.

Also trying to unlock your phone by jailbreaking is also illegal.

However, in reason for jailbreaking is not recommended by Apple and will void warranty.

No, but it is unsupported.

In the US, jailbreaking is not currently illegal. Unlocking, however, is.

Jailbreaking will void any warranty, forfeit any right to support, and could end up bricking your phone.

If you have the intent of using it to unlock your iPhone, then yes it is. Other than that, it is against the license agreement you agreed to in order to use the iPhone. It cannot be discussed here further for those reasons. It also causes many problems, such as: http://support.apple.com/kb/ht3743

The reason why that Apple is against this is because the people who write the apps that allow a JB look for vulnerabilities in the OS and then use those to get into the system to apply the JB.

For the most part, the hackers are allowing Apple to make the OS more secure by patching up those holes each time they release a JB. The next OS release patches up the holes that allow the current JB.

Incorrect, the security updates released for jailbroken iPhones generally have nothing to do with iOS updates from Apple. More updates are required for jailbroken iPhones due to the access to a file management system and removing sandboxing. A jailbroken iPhone is inherently riskier than iOS due to removing sandboxing.

It is not illegal. And unsupported wouldn't be a good word for it. Many people who are wealthy enough, like me (sorry, apple) donate to the cause. I am fully supportive of the wonderful jailbreaking experience. But I don't reccomend the misuse of cydia's wonderful apps. If you use it, please use it respectfully and responsibly. Don't use it to get apps or 3/4g for free. Use it to boost your max volume, or for brightness shortcuts.

NO,but it will void your warranty and it could be more eaiser to get a virus on it