iH8snow pushed out an update to Sn0wbreeze v2.9.5 that supports the latest iPhone 4 5.1.1 9B208 IPSW and also fixes location services issues that iPhone 3Gs users have been having.
A5 devices are still not yet supported, but all other A4 devices can be used to extract custom 5.1.1 IPSW files. Download Sn0wbreeze 2.9.5 and iPhone 4 GSM 5.1.1 (9B208) from the links given below and follow the guide posted here to use Sn0wbreeze to make Custom (pre-jailbroken) IPSW files.
Update # 1:
We have made an iPhone 4 5.1.1 (9B208) custom IPSW file using Sn0wbreeze’s simple mode, which means once you restore to it you will have Cydia on your device and your baseband will be preserved.