Is It Legal to Jailbreak and Unlock Your Cellphone? Copyright Office Officially Says, "Yes."

"Apple can still say jailbreaking voids your warranty, but you're not doing anything illegal by jailbreaking your phone and installing apps not approved by Apple. Other good news: Unlocking cellphones (to use your phone with another carrier) was deemed legal in this ruling, as was circumventing DVD DRM to use the video for educational purposes, documentary film-making, and non-commercial videos."