If you are having iPhone 4, iPhone 3GS or iPhone 3G that are already jailbroken iOS 5.0.1 and you want to unlock through recently released Ultrasn0w 1.2.5 you can follow the steps below:
UltraSn0w 1.2.5 Supported Basebands are as under:
iPhone 4: 01.59.00
Remember your device should be Jailbroken so that you can use Cydia for unlocking using UltraSn0w 1.2.5, you can visit this article to jailbreak now.
Steps for Unlocking are:
1. Tap Cydia
2. Tap Manage —–> Sources
3. Tap Edit ———> Add Button
4. Type Following URL and Tap Add Source
5. Now search for Ultrans0w in Cydia and install it
6. Reboot your device
Now your device is unlocked on iOS 5.0.1.