Purplesn0w and Purplera1n are both very powerful tools for jailbreaking an iPhone, and this video will show you how to use them! Before you begin, it's important to know that this tutorial will only work if you have 3.0 firmware. If not, download it, or check out another video that covers 3.0.1.
Step one- Go to www.purplera1n.com
2- Download for Mac or Pc then open file.
3- Click "make it rain"
4- Open Freeze and install cydia. Reboot.
5- Add apt.geohot.com to sources
6- Install com.geohot.purplesn0w
7- Turn 3G off and reboot.
8- Insert SIM and enjoy.
If you previously jailbroke your iPhone 3GS and have problems then you should restore it to original 3.0 Firmware. Download with Firefox to get in IPSW.