A jailbroken phone is an iPhone which has been modified to allow the user to install applications which are not released through Apple's App Store. The term “jailbroken” can also be used to refer to iPods which have been modified for similar reasons. This practice is not condoned by Apple, which regards it as copyright violation, and it will void the warranty on the phone, which means that if the phone is damaged or the software is corrupted, the user has no recourse through Apple.

Almost as soon as the iPhone was released, Apple was being criticized for forcing users to go through the App Store to access applications, and for restricting applications available through the App Store. Apple's defense of the App Store was that it ensured that all applications loaded by users onto Apple iPhones were safe for use, reducing the risk of spreading viruses or corrupting the software. Critics pointed out that applications which rivaled Apple products were not available, even though many were safe for use, and some critics simply disliked the idea of being told what they could and couldn't download. As a result, shortly after the iPhone's release, people were jailbreaking their phones and providing information to others who were interested in jailbroken phones.

A jailbroken phone is not the same thing as an unlocked phone. When a phone is unlocked, it means that it can work on any mobile network, and “unlocking” can refer to a wide variety of phones. When a phone is jailbroken, it specifically allows the user to install applications from sources outside the App Store. Should other producers of mobile phones follow Apple's lead with the App Store, presumably innovative techies will figure out how to jailbreak them as well.

A number of guides to producing a jailbroken phone can be found online, with varying degrees of reliability. People who are not experienced may encounter problems following such guides, and they could damage their devices so that they can no longer be used in the process. The directions for jailbreaking also vary depending on which version of the phone someone is using, and which version of the software is being utilized, making it important to read them thoroughly before starting, and to confirm that the directions are appropriate for the phone in question.

Sites which provide information about iPhone hacks such as those which can produce a jailbroken phone usually come with extensive disclaimers warning users that they proceed at their own risk. People are reminded that they cannot take a jailbroken phone in for service or repairs, and that they may have difficulty updating the software on a jailbroken phone. Those who lack expertise in this area may want to spend some time reading forums and reputable tech sites to learn about the most likely sources of accurate instructions for jailbreaking a phone.