The Apple iPhone is one of the most popular smartphones on the market, thanks to its sleek design and extensible operating system. As of 2010, the iPhone was available only to AT&T customers, leaving users of other carriers out of the picture. It is possible to unlock the iPhone for usage with other carriers, but it's first necessary to "jailbreak" the phone. Jailbreaking is the process of opening the iPhone operating system to manual configurations that are not explicitly supported or approved by Apple. Once this is done, the device can be unlocked and virtually any mobile phone SIM card can be used.
Tap "Safari" to launch the iPhone Web browser.
Navigate to JailbreakMe (see Resources).
Swipe the "Slide to Jailbreak" slider to download and install the JailbreakMe software to your iPhone.
Swipe "Enable 3G" to "Off."
Return to the home screen and tap "Cydia."
Tap "Edit" and then "Add."
Type "repo666.ultrasn0w.com" then tap "Add Source." Tap "Done."
Tap the search box at the top of the screen in Cydia and type "ultrasn0w" then tap the application icon.
Click "Install" and then "Confirm."
As of September 2010, the iOS has been updated to 4.1, which greatly restricts the exploits used to jailbreak and unlock the iPhone. It is recommended that iOS not be updated beyond 4.0.1 if you wish to jailbreak and unlock your iPhone.
Unlocking your iPhone can void your warranty.