Under the Digital Millennium Copyright Act, jailbreaking iPhones is legal in the United States, although Apple has announced that the practice "can violate the warranty".
In 2010, in response to a request by the Electronic Frontier Foundation, the U.S. Copyright Office explicitly recognized an exemption to the DMCA to permit jailbreaking in order to allow iPhone owners to use their phones with applications that are not available from Apple's store, and to unlock their iPhones for use with unapproved carriers. Apple had previously filed comments opposing this exemption and indicated that it had considered jailbreaking to be a violation of copyright (and by implication prosecutable under the DMCA). Apple's request to define copyright law to include jailbreaking as a violation was denied as part of the 2009 DMCA rulemaking. In their ruling, the Library of Congress affirmed on July 26, 2010 that jailbreaking is exempt from DMCA rules with respect to circumventing digital locks. DMCA exemptions must be reviewed and renewed every three years or else they expire. In 2012, the Copyright Office renewed the jailbreaking exemption for phones but declined to approve a new exemption for tablet computers such as iPads, due to the vague definition of "tablet" in the proposed exemption. The Copyright Office also renewed the 2010 exemption for unofficially unlocking phones to use them on unapproved carriers, but restricted this exemption to phones purchased before January 2013.
Tim Wu, a professor at Columbia Law School, argued in 2007 that jailbreaking is "legal, ethical, and just plain fun." Wu cited an explicit exemption issued by the Library of Congress in 2006 for personal unlocking, which notes that locks "are used by wireless carriers to limit the ability of subscribers to switch to other carriers, a business decision that has nothing whatsoever to do with the interests protected by copyright" and thus do not implicate the DMCA. Wu did not claim that this exemption applies to those who help others unlock a device or "traffic" in software to do so. In 2010 and 2012, the U.S. Copyright Office approved exemptions to the DMCA that allow iPhone users to jailbreak their devices legally. It is still possible Apple may employ technical countermeasures to prevent jailbreaking or prevent jailbroken phones from functioning, but it will not be able to sue users who jailbreak. It is also unclear whether it is legal to traffic in the tools used to make jailbreaking easy.