As Yellowsn0w is still in beta phase, you would expect it to contain bugs here and there. In fact, there are lots of reports that saying attempt to unlock iPhone 2G or iPhone 3G with firmware OS version 2.2 at baseband 02.28.00 does not work as advertised. Which means the iPhone still lock to a single telco, i.e AT&T in US despite using Yellowsn0w after using QuickPwn to jailbreak it.
But iPhone Dev Team is working quickly to fix all the issues on soft unlock the iPhone. As such, new versions of Yellowsn0w has been updated and released in quick succession, firstly 0.9.1 and then to current version of 0.9.4.
Yellowsn0w 0.9.1 extends the delay for SiM card to initialize to 60 seconds, where unlocker has to wait a full minute after you see homescreen, then reinsert sim card. Yellowsn0w eliminates the one-minute delay step and fixes the issue without the need to wait a minute and then replug the SIM. However, if you don’t see your carrier when your homescreen comes up, you may still need a sim reinsert (for now).
Yellowsn0w 0.9.5 has also been released,fixing quite a few problems including some STK issues.
The Yellowsn0w 0.9.5
0.9.4 can be downloaded fromm the following URL using Cydia or Installer.
Cydia source: http://apt9.yellowsn0w.com/
Installer repo: http://i.yellowsn0w.com/
Update: Yellowsn0w has been replaced with Ultrasn0w.