If you have your 3.1.3 SHSH saved, then you will be able to downgrade to 3.1.3, jailbreak with Spirit, and unlock with ultrasn0w. If you do not have your SHSH saved, you will have to wait for the upcoming jailbreak before you can unlock.
Note: if you do not know what SHSH are, search. There are plenty of threads on here that will tell you what you need to know.