The US government has legalized jailbreaking, rooting, and the unlocking of cellular telephones by adding the respective provisions to the Digital Millenium Copyright Act among the many new exemptions added to relax the stringent copyright laws. Additionally, AppleInsider reports that other exemptions announced Monday allow people to break protections on video games to investigate or correct security flaws; allow college professors, film students and documentary filmmakers to break copy protection measures on DVDs to embed clips for educational purposes, criticism, commentary and noncommercial videos; and allow computer owners to bypass the need for external security devices (dongles) if the hardware no longer works and cannot be replaced.
In regards to jailbreaking, the DMCA now says "Computer programs that enable wireless telephone handsets to execute software applications, where circumvention is accomplished for the sole purpose of enabling interoperability of such applications, when they have been lawfully obtained, with computer programs on the telephone handset."
Jailbreaking is the process used on the iPhone and iOS devices to allow apps that may not have gain Apple's App Store approval to operate on the device and unlock other features of the iPhone that are not officially made available, such as call blocking applications and adding a "Today screen" to the lock screen of the iPhone as well as customized widgets. The process of similarly unlocking powerful features is known as rooting on Android OS devices. Additionally, unlocking a handset will allow users to bring their GSM-compatible handsets to another carrier. In the US, AT&T iPhones could then be unlocked to use on T-Mobile though since the iPhone only supports AT&T's 3G networks, unlocked iPhones would only work on T-Mobile's EDGE network for data