Just got the iPhone 4 and I can't wait to jailbreak it. I'm on AT&T and don't need to unlock the phone, I just want Cydia so that I can install SBSettings. I've only use the Spirit jailbreak once on my iPad it works wonders.
Spirit as it stands will never come out for iOS 4. The Spirit jailbreak uses a userland exploit that no longer exist in 4.0. If Spirit is updated it will have to use a completely different exploit and it will no longer be a userland jailbreak.