Short version:
What iPhone-dev Team said :

* Short version :

ultrasn0w version 0.9 is out!  We believe it solves pretty much all of the various random issues that have been reported.  Its features include:

    * Works on both 3G and 3GS
    * Works on hacktivated devices
    * Works regardless of how you jailbroke your device
    * Doesn’t patch any mach-o binary whatsoever.  (Doesn’t require a separate patch as each new firmware comes out).
    * Doesn’t install any additional daemon
    * Has no race conditions, no popups about “Missing SIM”, no network issues
    * Is almost 7000 times smaller than its nearest competition :)
    * Is available now via Cydia.  Source repo is (that last “0” in ultrasn0w is a zero!)