If you own an iPhone, you should jailbreak it.
iOS jailbreaking, further on referred to as jailbreaking, is the process of removing the limitations imposed by Apple on devices running the iOS operating system through the use of custom kernels (software). Such devices include the iPhone, iPod and iPad.
Jailbreaking allows users to gain root access to the operating system, thus allowing iOS users to download additional applications, extensions and themes that are unavailable through the official Apple App Store. A jailbroken iDevice running iOS can still use the App Store, iTunes and perform normal functions; such as making telephone calls or text messaging with no problems to the normal functionality of the device.
There are two types of jailbreaks: tethered and untethered. A tethered jailbreak requires a reboot from a computer each time it requires to be booted (i.e. when you power off and on). An untethered jailbreak allows the device to be powered without computer assistance.
Jailbreaking is a form of privilege escalation, allowing your device to function more freely on otherwise restricted software (iOS). Jailbreaking is necessary if the user intends to run software that is not authorized by Apple—not unlike Androids which allow root access.
One of the main reasons for jailbreaking is to expand the features limited by Apple and it’s App Store. Most jailbreaking tools automatically install Cydia, a native iOS APT (Advanced Packaging Tool) client used for finding and installing software for jailbroken iOS devices. Since software programs available through Cydia are not required to adhere to App Store guidelines, many of them are not typical self-contained apps but instead are extensions and customizations for iOS and other apps.
Users install these programs for purposes including personalization and customization of the interface, adding desired features and fixing annoyances, and making development work on the device easier by providing access to the file system and command-line tools. Some users look to software outside of the App Store to express opposition to Apples censorship of content through the app approval process.
A popular customizations is the ability to tether the internet provided through carriers onto other devices. Carriers normally charge for this feature but if an individual has an unlimited data plan, why should they not be allowed to use it for other devices?
Another popular download is the ability to use FaceTime over 3G, which on current iOS devices is only available to users over a Wi-Fi connection.
But perhaps the greatest “tweak” included with jailbreaking is the ability to test out apps before purchasing them through an application called Installous, which allows you to download paid apps for free directly to your iDevice.