Here’s a short video of yellowsn0w in action. It works much faster than the first version and all T-Mobile USA customers should be happy! Check the iphone-dev team blog for the source URLs to the Cydia / Installer repos.
yellowsn0w 0.9.5 beta demonstration from theiphoneproject on Vimeo.
Let us know if it worked for you! If you guys are still having trouble, the amazing iphone-dev team have setup a bug reporter/tracker system. It can be accessed here.
Quick Update:
Everytime I reboot the SIM isn’t recognized (it just searches for network). If you turn airplane mode ON and then off (Settings > Airplane Mode: ON), it will start working.