As you may already know the iPhone 3.1.2 jailbreak and unlock are fully functional and running strong thanks to geohot’s amazingly simple blackra1n software available as a free download at http://blackra1n.com.
The steps are simple.
1. Download blackra1n for your MAC and save it to your desktop
2. Restore your iPhone 3G or 3GS via the latest iTunes 3.1.2
3. Close iTunes
4. run blackra1n
5. click make it rain
6. wait for iPhone to reboot
7. click the blackra1n icon on your iphone and select at least the bottom icon to unlock the phone for T-mobile
8. reboot 2 times
9. enjoy your jailbroken unlocked iPhone


The iPhone 3G, 3GS 3.1.2 jailbreak/unlock for T-Mobile on a MAC running OS X by UndergroundcityStudios, unless otherwise expressly stated, is licensed under a Creative Commons Attribution-Share Alike 3.0 United States License.

Cool, I hope my site helps people out.