And keep in mind that this only for iOS 5 or 5.0.1, those who have Furiousmod installed on their iOS 4.1 or 4.2.1 devices is recommended not to upgrade to this Furiousmod version and step out from this tutorial. Because this update seems to contain some issues on iOS 4.
Unlock iOS 5.0.1 Using Untethered GEVEY Ultra FuriousMod 2.0
Jailbreak your iPhone 4 on iOS 5 or 5.0.1 first using Redsn0w or Corona.
Install FuriousMod 2.0 on iOS 5.0.1 device.
1. And then add this repo URL source in Cydia: http://cydia.furiousmod.com.
2. And then find or search FuriousMod, once you found it and then install it. The updated version is 2.0.
3. Restart your iPhone 4, after FuriousMod is successfully installed. And be sure Gevey Ultra is already insterted with a GSM sim.
4. After your Device boots, you will see FuriousMod take unlock process in background, it takes about 45 seconds, then you will see that your iPhone 4 get the network.