WASHINGTON: President Barack Obama signed a bill into law on Friday making it legal once again to unlock a cellphone without permission from a wireless provider, so long as the service contract has expired.

Copyright law prohibits circumventing digital locks on technological devices. But for several years, cellphones were granted an exemption by government copyright lawyers as a way of making it easier for consumers to change carriers and recycle old phones.

Then under industry pressure, the Library of Congress — which oversees copyright law — agreed to let the exemption lapse as of January 2013, infuriating consumer advocates who say phone owners should be able to do whatever they want with a device once a contract expires.

Wireless providers have said digital locks on cellphones protect their business model: phones are often sold at a steep discount in exchange for long-term service contracts. If a consumer doesn't want to be tied to a particular carrier, they can always pay the higher price of a device that's already unlocked, industry officials say.

The Library of Congress agreed with that logic in its latest ruling. But public backlash was fierce and several wireless providers responded by outlining a set of voluntary industry standards for unlocking.

Consumer advocates said the process remained slow and cumbersome. They wanted tech-savvy consumers to be able to unlock phones by themselves or use a third-party, which the new legislation allows.

The bill doesn't apply to other wireless devices such as tablets, but directs the Library of Congress to consider whether consumers should be allowed to unlock those as well.

The legislation is only effective until the Library of Congress issues its next ruling, most likely in late 2015. But consumer advocates hope that the popular legislation will be enough to convince the federal office that it should continue to allow unlocking.

CTIA-The Wireless Association, which represents major wireless providers including AT&T, Sprint Corporation, T-Mobile USA, US Cellular and Verizon Wireless, said in a statement: “Even though the vast majority of Americans enjoy upgrading to new devices once their contract terms are fulfilled, we recognise that some consumers may want to unlock their devices to move to another carrier.”

It noted, however, that even though the phone is unlocked it might not work on other carriers because platforms and spectrum holdings vary.