All three devices are powered by the same iOS (formerly called iPhone OS) operating system which was developed by Apple itself, and which is based on another operating system made by the Mac OS. The iOS contains Mac OS parts integrated in its own system, like the animation graphics. The problem with this operating system is that Apple have implemented certain boundaries which users can't normally pass, regarding access to different aspects of the phone. Hackers have discovered a way to get rid of those boundaries, by using something called Jailbreaking.
By jealbreaking the iPhone, iPad, or iPod Touch, one is granted root access to the command line, and in the same time get rid of Apple's usage and access limitations. One jailbroken, an iOS device, you can download extensions and themes that weren't available through the AppStore, via installers such as Cydia, or even change the operating system. However, with all these new possibilities, you may think that there is a bad side to i, such loosing access to original AppStore material. Well, the thing is that you cannot only install new themes and operating systems, but you can also use official Apple elements such as the AppStore, or perform all the normal functions of an Apple device, like calling, in the case of the iPhone.
Many people have the Jailbreaking phenomenon confused with SIM unlocking, which is totally different. By performing a SIM unlock, the user's iPhone will accept any SIM card that is given, avoiding possible carrier or network restrictions of the iPhone in your country. Under the DMCA of 2010, Jailbreaking an iOS device is perfectly legal, although Apple claims doing it will avoid the device's warranty. That being the only downside of jailbreaking, you can always go into iTunes and reverse he jailbreak process before going with your phone at a repair center when it needs to be fixed.
Jailbreaking an iOS device is also legal in several countries from the EU. The first jailbreaking method was discovered on July 10, 2007, when an American teenager wanted to stay on T-Mobile, although Apple locked their iPhone device on American carrier AT&T. One month later, the first third party game was released for the iPhone and iPod Touch. Later, another jailbreaking method was found, which led to a cat and mouse game between Apple who was trying to patch the security breaches, and the hackers, who were trying to exploit them.