On Sunday, new legislation on exemptions to the prohibition against circumvention of technological measures that effectively control access to copyrighted works – often referred to as 'jailbreaking' – will enter into force in the United States. Under the new rules, jailbreaking mobiles phones is legal, but jailbreaking tablets is not.

In 2010, jailbreaking of mobile phones was already legalized, provided that it was accomplished for the sole purpose of enabling interoperability of software applications that have been lawfully obtained. For example, iPhone users can only run apps from Apple's iStore, unless they jailbreak their phones. Besides, it was allowed to unlock the firmware or software of a mobile phone in order to connect to a wireless telecommunications network.  http://www.copyright.gov/1201/2010/Librarian-of-Congress-1201-Statement.html 

Under the new rules, jailbreaking a mobile phone to run legal apps that otherwise won't run will still be legal. However, unlocking a mobile phone will be illegal from January 2013.

Despite many proponents, the jailbreak exemption won't be extended to tablets. According to the Register of Copyrights, this class of devices "is broad and ill-defined, as a wide range of devices might be considered 'tablets', nothwithstanding the significant distinctions among them in terms of the way they operate, their intended purposes and the nature of the applications they can accomodate." For example, e-book readers, laptop computers or handhald video game devices might be considered as tablets. 

iPad users probably won't be happy with the new rules. Just as iPhone users, they can only run apps from the iStore on their devices. For Android users, the restriction will be less relevant, as they can run apps from outside the Google Play Store anyway.

Read the announcement of the new legislation here.

Read more about jailbreaking on FutureOfCopyright.com:

• Should jailbreaking a mobile phone continue to be exempted from copyright infringement in the U.S.?
• PlayStation 3 hacked, encryption keys exposed
• Apple dropped jailbreak detection API from iOS 4.2

Sources: Tweakers.net, U.S. Copyright Office