Earlier this month Apple pushed iPhone firmware 3.1.3 , which updates the baseband to 05.12.01. You can jailbreak the new firmware with redsn0w, pwnagetool or sn0wbreeze, but at the moment it is impossible to unlock ( pwnagetool and sn0wbreeze lets you create custom .ipsw firmwares to jailbreak your iDevices and not update the baseband ) .
If you didn’t update, you didn’t miss a single thing, but maybe the time will come when an update or a new app will ask you for firmware 3.1.3. So , will you update? No, you can use a nice little tweak found in Cydia to fake your firmware to 3.1.3. This will not affect in any way your jailbreak or unlock.
First you need to load Cydia and add this source: http://cy.sosiphone.com/ . Once the source is loaded, simply search for Fake 3.1.3 and install it. Once you reboot your iDevice, go to Settings>General>About and you should see Version: 3.1.3 (7E18)
NOTE: you do not need this tweak, unless an app that you really want requires the latest Apple update.