I know people are still on the lookout for ways to unlock their iPhone 3Gs and now some people are claiming they've done with just a YESSIM sim card. No software needed. The only prerequisite is that you have a jailbroken iPhone. 
So what's the downside? I still don't see any proof. Sure, there's a video--and it's posted below--that showcases this YESSIM unlocking method. But the site's FAQs and information are vague at best. Plus, the video doesn't really show all that much.
What will it take for a video showing this unlocking process for real to show up online? Until then, I'm not convinced.
[via The iPhone Blog]
I have tried it, but it is not working very stable. my friend has unlocked his iPhone 3G with a card called Universal Sim and told me it is working well.
Yessim does work. I have a 3G iPhone bought via ATT running in Japan. I bought this handset as the Japanese won’t sell it to us foreigners stating ‘for new customers only’ — which is not correct. Anyway, I used a Yessim and reprogrammed it using their USB unit with updated settings and hey presto– it does unlock the unit. Phonecalls in / out work fine plus SMS. Of course, if you want the settings of your operator to use the Internet, they must be added separately. Yessim works :-)
Thanks