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.