Yes. You will need two applications. You go to blackra1n.com and download tht program to jailbreak.
Once you're jailbroken and your iPhone has restarted, open the "blackra1n" app on your iPhone. Install "Cydia".
Once Cydia installs, go through the motions. Follow all of it's prompts. Let your phone reboot.
Open Cydia again, and then do a search for "BootNeuter". That will be how you unlock your original (2G) iPhone.
If you have any questions, feel free to PM me.