Last October, the Librarian of Congress issued a temporary exemption to legislation that outlaws the unlocking of cell phones. The exemption allows for phones owned or purchased before January 26, 2013 to be legally unlocked by the user. After the deadline, users will have to request permission from their carriers to unlock handsets, or be in violation of a federal law.
Carriers lock smartphones as a way to prevent their customers from getting a cellular plan with a different company. Users unlock phones when they want to switch carriers, sometimes after the phone's original contract has run out, or so they can use it when going abroad.
The Librarian of Congress determined that consumers have a number of alternatives to unlocking devices, including buying devices that come already unlocked.