How to unlock iPhone 4 running on iOS 4.1 with old baseband: 01.59.00 using the Ultrasn0w1. Visit this link, to update to iOS 4.1 and keep the old baseband.
2. Jailbreak your iPhone 4 using LimeRa1n.
3. Open Cydia and head to Manage > Source > Edit and then click on Edit to add the following url:
4. Install the repo, wait till the installation to finish, afterward back to Cydia and search for Ultrasn0w, then hit on it, it will then doing the automatic installation and then restart your iPhone.
5. Congratulation your iPhone 4 is not a jailbroken iPhone, it's also the unlocked device with the old baseband 01.59.00