Sn0wBreeze 3.1.3 update is now available for download allowing users to create custom 3.1.3 IPSW restore files while retaining the older baseband so they can still enjoy existing blacksn0w or ultrasn0w iPhone unlocks.

To get iPhone OS 3.1.3 with jailbreak and carrier-unlock all you need to do it to create a custom IPSW file using Sn0wBreeze 3.1.3 (download link after the jump) and restore you iPhone with this newly created IPSW file having older baseband.