I might be picking up an iPhone 3G later used and was just wondering what numbers I need to look at and what they need to be to make the phone unlockable.
Correct, you don't want to get one that has OS 2.2.1 and Baseband 02.30.03 since the baseband is not unlockable using Yellowsn0w. You also might want to check the warranty status by checking the liquid indicator sensors in the earphone jack and the dock. Pink or Red, no warranty for you.