Pretty much everything you need to know is in the stickies, specifically this post on consolidated rev a tutorial
http://forum.ppcgeeks.com/showthread.php?t=24979
Those are the exact instructions I followed when I did mine. Long story short, unlock with ImCoKeMaN 2.31 unlocker, flash with any rom that includes a 3.x radio (Alltel or leaked Sprint), then you can re-flash again with any 3.x rom of your choice. That's just a summary of the process. There are many details to pay attention to so you don't brick your phone. Following the directions in the mentioned thread carefully is key.