except iOS 4.1, or wait for a public jailbreak for iOS 4.1.
Step 1: Download iPhoDroid R13k at the bottom of the page
Step 2: When launching the application on Windows 7 you may have a strange error says "Apha Expired! New Release available", it can be solved by changing the date a month back (i.e. if the date of the system is Sep. 13 then change it to Aug. 13)
Horaya! Now, you have an iPhone 3G / 2G unlocked on Android Froyo 2.2, iPhoDroid R13k can be downloaded from the links below:
Download iPhodroid R13k for iPhone 3G (Windows)
Download iPhodroid R13k for iPhone 2G (Windows)