iphone 3gs T-mobile

How to jailbreak iphone 3Gs on 4.0 and 4.0.1:
1.go to safari on your itouch or iphone
2. type in: jailbreakme.com
3. on the website there should be a slider that says," slide to jailbreak
4.slide and wait
5. once its done it should say" cydia has been added to your desktop have fun!"
6. check! cydia should be added to your desktop!
how to unlock:
1. go to cydia
2. tap on manage
3.tap on sources
4.under "installed by package" you should see "repo666ultrasn0w.com"
5. tap on it
6. modify and install.
6. congratulations your iphone or ipod is now jailbroken and unlocked.

For all those noobs out there:

Jailbreakingis a process that allows iPad, iPhone and iPod Touch users to run third-party unsigned code on their devices by unlocking the operating system and allowing the user root access. Once jailbroken, iPhone users are able to download many extensions and themes previously unavailable through the App Store via unofficial installers such as Cydia. A jailbroken iPad, iPhone or iPod Touch is still able to use the App Store and iTunes.

Jailbreaking is different from SIM unlocking, which, once completed, means that the mobile phone will accept any SIM without restriction on, for example, the country or network operator of origin. Jailbreaking, according to Apple, can void Apple's warranty on the device,[1] although this is quickly remedied by restoring the device in iTunes.
Cydia founder Jay Freeman estimates that over 10% of all iPhones are jailbroken.