As we all know, the current version of Ultrasn0w doesn’t support iOS 4.3.1. Though with the help of Ultrasn0w Fixer you can install Ultrasn0w 1.2 on your iPhone 4 & iPhone 3GS (temporary fix) and start making & receiving calls. But, still it carries a tiny little bug, where you will notice a single signal bar, even though you have full cellular signal.
Just a little while ago, MuscleNerd of The iPhone Dev Team has confirmed that they will be releasing an updated version of Ultrasn0w 1.2.1 today (if all goes well)
This updated version will support iOS 4.3.1 and it will also display the accurate signal strength on your iPhone 4 & iPhone 3GS.
Keep in mind that, this version of Ultrasn0w does not unlock any new basebands. That means, it only support the following basebands (04.26.08, 05.11.07, 05.12.01, 05.13.04, 06.15.00, and 01.59.00).
iPhone Users with the above mentioned baseband, have to use PwnageTool 4.3 / Sn0wbreeze 2.5 to preserve your baseband while upgrading to iOS 4.3.1 (if you haven’t already)