This kind of unlock got a little bit old and unsupported by newer iPhone models. Ultrasn0w is a program created way back by the iPhone Dev Team which provides an unofficial carrier unlock for jailbroken iPhones which means that you can use any sim card in your iPhone.
Ultrasn0w unlocking works with iPhone 3G / 3GS and the iPhone 4. Supported basebands are:
- iPhone 4 running on baseband 01.59.00
- iPhone 3G/3GS running on basebands 04.26.08, 05.11.07, 0.5.12.01, 05.13.04 or 06.15.00
Ultrasn0w 1.2.4 (and later) uses the same AT+XAPP command exploit found in the 05.13.04 baseband to update the iPhone 3G and 3GS’s baseband to version 6.15.00 (found in the iPad 3G).