The Library of Congress' Copyright Office also ruled that iPhone users can bypass Apple's access controls to download and run applications not approved by Apple.
The rulings refute Apple's contention that iPhone buyers are licensees of the technology, not owners, and thereby bound by the company's licensing agreement.
Apple also argued in submissions to the US Copyright Office that "jailbreaking" iPhones circumvented access controls designed to protect consumers and Apple from harm.
But the Copyright Office said jailbreaking any smartphone to make the operating system on that phone interoperable with an independently created application is fair use.
The rulings were made in response to a request for exemptions to the Digital Millennium Copyright Act by the Electronic Frontier Foundation (EFF), a consumer advocacy group.
The EFF said the rulings recognized that the primary purpose for the locks on smartphones that bind users to a particular carrier or applications are to limit competition, not to protect copyrights.
This story was first published by Computer Weekly