MuscleNerd has tweeted that an updated version of Ultrasn0w would be released tonight. The unlock 4.3.1 will be compatible with iPhone 4 and iPhone 3GS. Using this update, users will be able to first upgrade to 06.15 Baseband and then would be able to downgrade to 05.13 Basebands. This surely is an important update as users on Basebands 05.14, 05.15, 05.16 don’t have any Unlock available till now. These users would be able to update their Basebands to 06.15 and then can downgrade to 05.13 for an Unlock.