On his blog today, Geohot announced that he will be taking a shot at an iPhone 4 compatible jailbreak, and he's calling it Limera1n. He doesn't say when the release will go public, but he does say not to bug him about it. That's all we know for now.
http://iphonejtag.blogspot.com/2010/07/meh.html
http://iphonejtag.blogspot.com/2010/07/meh.html