Finally, the iPhone 3G has been unlocked, with those devious types at the Dev-Team responsible once more. The unlocked, dubbed “yellowsn0w” (don’t eat it, download it!), is available now and works with software version 2.2 – in fact, it requires that your iPhone 3G is running it.
The release isn’t fully finished at present, and is still technically a beta, so you might experience one or two issues, but in general it should let you use any SIM card with an iPhone 3G. Happy iPhoning!