Looks like msftguy is on fire. His latest patch is the blacksn0w unlock for iOS 4. He earlier patched blacksn0w for iPhone OS 4.0 Beta and was also responsible to patch PwnageTool to jailbreak iOS 4 on iPhone 3GS. Patch works only for baseband 05.11 hence you need to have preserved your baseband. To preserve baseband 05.11, you should jailbreak iOS 4 with PwnageTool. Here is the video showing blacksn0w unlock for iOS 4 in working:

We’ll still recommend that you should wait for the official update of iOS 4 on June 21 as dev team have promised the complete package including Sn0wbreeze 1.6 and official PwnageTool update with ultrasn0w or blacksn0w unlock. You can also jailbreak iOS 4 on iPhone 3G and iPod Touch 2g with redsn0w 0.9.5 B5.