Hi in this video i´ll show you how to jailbreak and unlock your Iphone 3G/S with Firmware 4.2.1.
So your phone must be on 4.2.1.
Unlockable basebands are:
06.15.00 ( IPAD BASEBAND )
If you have any of those basebands you can just jailbreak and unlock with Ultrasn0w.
If you are not on one of These , follow this tutorial.
Just follow the steps shown in the Video. Here is also a written tutorial:
In the next Video i´ll Show you how to downgrade your baseband again to get GPS working properly !
If you get no Service , try the whole Thing again, it will work !