According to the EFF (and just about every other tech blog in the known universe), the Library of Congress and the Copyright Office have ruled jailbreaking is legal.
When one jailbreaks a smartphone in order to make the operating system on that phone interoperable with an independently created application that has not been approved by the maker of the smartphone or the maker of its operating system, the modifications that are made purely for the purpose of such interoperability are fair uses.
Also, in a ruling somewhat overshadowed by the jailbreaking issue, they handed down something of a smack-down to Hollywood:
EFF also won a groundbreaking new protection for video remix artists currently thriving on Internet sites like YouTube. The new rule holds that amateur creators do not violate the DMCA when they use short excerpts from DVDs in order to create new, noncommercial works for purposes of criticism or comment if they believe that circumvention is necessary to fulfill that purpose. Hollywood has historically taken the view that “ripping” DVDs is always a violation of the DMCA, no matter the purpose.
Even though the DMCA was/is a huge step backward for consumer rights and individual liberties, these rulings are something of a giant step forward. Here’s hoping the pendulum keeps swinging our direction.
