As of June 2015, it is not illegal to jailbreak an iPhone in the United States, explains Cult of Mac. However, under the Digital Millennium Copyright Act it is illegal to jailbreak an iPad.
Jailbreaking an iOS device allows installation of applications, modifications and hacks to the Apple device that the App Store normally does not allow, according to Cult of Mac. "Jailbreaking" should not be confused with "unlocking." Unlocking a smartphone is a process that frees the phone for use on any wireless provider instead of the provider through which the phone was purchased. It is illegal to unlock any smartphone purchased after January 26, 2013.