Seems like the iPhone dev team has been busy serving jailbreak and unlock community because the name is consecutively delivering many updates for both their jailbreak and unlock tools these days.
These are the baseband and iPhone models supported by Ultrasn0w 1.2.7:
- iPhone 4 on baseband 01.59.00
- iPhone 3G/3GS basebands 04.26.08, 05.11.07, 05.12.01, 05.13.04, and 06.15.00
Therefore if your existing firmware is not iOS 5.1.1 you can update to the said firmware now, because this Ultrasn0w can now unlock the iOS 5.1.1 firmware. But if your baseband is the new or not on the supported list above, then your are out from this excitement. so sorry :(.
To get Ultrasn0w 1.2.7 simply launch Cydia, as this tool can be found there, and if your iPhone is already unlocked with this tool previously, you should be informed about the update once Cydia is launched.