Good news for those who are facing 1-signal-bar issue after jailbreaking their iPhone on iOS 4.3.1. MuscleNerd, the most vocal member of iPhone Dev-Team just confirmed that he has managed to fix the signal bars issue which was mainly experienced by those iPhone users who have old basebands and tried to jailbreak iOS 4.3.1 using PwnageTool 4.3 or Sn0wbreeze 2.5.
Those iPhone users who do not rely on an unlocked iPhone and are running newer basebands (05.16.01, 05.16.02, 04.10.01) will not face signal bars issue. This issue occurs only on those iPhones who are jailbroken on iOS 4.3.1 and have preserved their old basebands (01.59.00, 02.10.04, 03.10.01) using PwnageTool or Sn0wbreeze. Even if you do not rely on an unlocked iPhone and want to preserve your current baseband while upgrading to iOS 4.3.1, you might run into signal-bar issue. People usually preserve their old baseband even if they do not rely on an unlock, just to increase the resale value of their iPhone.
According to MuscleNerd, the fix for one signal bar issue will be available as an Ultrasn0w update in Cydia. MuscleNerd also intimated, not to confuse this Ultrasn0w update with the NCK unlock for iPhone 4. The new upcoming update of Ultrasn0w will NOT unlock iPhone 4 02.10.04, 03.10.01 or 04.10.01 baseband but will only fix original Ultrasn0w 1.2 on iOS 4.3.1.