Yesterday, the US Copyright Office made revisions to their rules- making it completely legal for anyone in the United Stated to jailbreak their iPhone. The new laws that you cannot be prosecuted for, regarding the iPhone, are as followed:

"(2) 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.

(3) Computer programs, in the form of firmware or software, that enable used wireless telephone handsets to connect to a wireless telecommunications network, when circumvention is initiated by the owner of the copy of the computer program solely in order to connect to a wireless telecommunications network and access to the network is authorized by the operator of the network."

You can find the entire list of the new "classes" here.

What this means? It is legal to allow software to run on your iPhone that you wouldn't be able to obtain without jailbreaking the phone, first. Also, jailbreaking can now be used legally to run your iPhone on a different (GSM) network.

Apple seems a bit unsound with these new rules. Fact is, they are now unable to ban third party programs that could possibly be harmful to one's iPhone experience. Their official response from Cult of Mac:
"Apple’s goal has always been to insure that our customers have a great experience with their iPhone and we know that jailbreaking can severely degrade the experience. As we’ve said before, the vast majority of customers do not jailbreak their iPhones as this can violate the warranty and can cause the iPhone to become unstable and not work reliably."