Unlocking is taking away SIM restrictions of the modem, permitting the use of iphone4 on any network. It means modifying its software so that the device works with several other service providers like T-Mobile.
An iPhone could be unlocked in two ways. Hardware Unlock and Software Unlock. Technically, hardware unlocking requires opening the phone. Being well trained with electrical engineering is recommended.
Another type is Software Unclock. It employs software to unfasten the phone from being trap in a single carrier. An example is an UltraSn0w. Unlocking using UltraSn0w is easily be done but there are rules to be followed.
UltraSnOw Unlock is a software creation for cracking locked iphone 4. This software obliges your device to undergo jailbreaking first with jailbreak tools of your choice like JailbreakMe, Greenpoison, Limera1n, Redsnow, Snowbreeze, and PwnageTool.
Here are the steps in Unlocking iPhone 4 and iPhone 3GS with Ultrasnow 1.2.1
1. Jailbreak the iOS 4.3.1 on your iPhone 4 with Pwnage Took 4.3 for Mac OS X or Snowbreeze 2.5 for Windows.
2. Once jailbreaking is done, unlock iphone 4, 3GS with ultrasnow 1.2 from Cydia.. launch Cydia application on the jailbroken iphone. After which, select Manage and proceed to Sources.
3. Choose Edit and click Add. Type the URL source in the sources field
4. Click Add Source and wait for it to upgrade.
5. Make a search for Ultrasn0w 1.2.1 in the search tap located at the bottom. Click it and press Install at the top.
6. Wait for the installation to finish. Reboot the unlocked iphone when done.
It is easily done. You can now switch your iphone into another carrier of your choice.