Originally Posted by skinnycow
i was successful in jail breaking my phone which was already a 4.2.1, but my cousin upgraded
If you need to unlock the phone, you first need to update the baseband to 6.15.00. Run redsnow, select your 4.3.1 firmware, then check 'install iPad baseband' when given the option. After it runs, your phone's baseband will be an unlockable 6.15.00. Install ultrasnow through Cydia (don't need to enter the repo like you did above, it's already entered for you) and it'll be unlocked.
Note that updating to 6.15.00 is permanent, you won't be able to simply hit 'restore' in iTunes and restore, and your GPS will stop working. But it is, as of now, the only way to unlock your phone.
EDIT: the above may not work for 4.3 or 4.3.1, in which case you'll need to downgrade to 4.2.1 or earlier (if at all possible, depends on the history of the phone), then update the baseband to 6.15.00, then update firmware to 4.3.1 if you'd like.