Ultrasn0w 1.2.1 to Unlock iOS 4.3.1 older baseband

The iPhone Dev-team just released ultrasn0w 1.2.1, an updated version of ultrasn0w. However, this updated version only fix compatibility issue on iOS 4.3.1 for older baseband (baseband 01.59.00), not for unlock 02.10.04, 03.10.01, 04.10.01

We have pushed out the 4.3.1 compatibility fix for ultrasn0w in Cydia — it is now at version 1.2.1. If you are not already at 4.3.1 and you need the unlock, please be sure you understand how to get to 4.3.1 using a custom IPSW that does not update your baseband. There are lots of guides for this (like at iClarified.com).

This is not a new unlock! It is to allow those who are already using ultrasn0w to use FW 4.3.1. It also fixes the signal bar issue for those who are not using the unlock but retain an older baseband intentionally.

AFTER INSTALLING ULTRASN0W 1.2.1, PLEASE REBOOT YOUR iPHONE using the normal “slide to power off” swipe. T-Mobile users in the USA also should disable 3G mode in Settings->General->Network.

A big thanks to @sbingner and @ronaldsb for helping with the testing of this update!

How-to update to ultrasn0w 1.2.1?

Open Cydia app, if Cydia find new updates, simply update your packages. Or you can tap Changes and refresh if Cydia didn’t find any update. Upgrade the ultrasn0w then reboot.
If you are T-mobile users in USA, you should disabled 3G mode in Settings → General → Network.