iOS 4.0 will be available for everyone on Monday (probably sometime in the evening) so take care of it DO NOT UPDATE to the new software until the jailbreak/decoding versions of Dev Team/geohot or whoever releases them appear.
redsn0w 0.9.x will activate all phones via jailbreak, so you will no longer need the operator's card to jailbreak your phone on iOS 4.0. The beta version of redsn0w does NOT hack phones, but the final version will, so stay calm because the card will no longer be needed to jailbreak, a fact confirmed by MuscleNerd in this tweet.
After the official release of iOS 4.0, decoding software will be released, but not as you expect: if the exploit found by the Dev Team in iOS 4.0 GM is also present in the final iOS 4.0, then the Dev Team will release an exploit for the version of baseband from iOS 4.0 and will no longer release a decoding solution for baseband 05.12.01 because it will no longer be needed. Why will it no longer be needed? If the Dev Team releases a decoding software for the iOS 4.0 baseband, then you will all be able to update to 4.0 directly from iTunes without any restrictions and you will be able to decode the phones without problems. If the iOS 4.0 GM exploit is not present in the final version, then the Dev Team will release a decoding solution for the 05.12.01 baseband, and later release a decoding solution for the iOS 4.0 baseband as well.
It is NOT known how long there will be jailbreak/decoding solutions for iPhone 4 because the new iPhone has new hardware and their "breaking" could take months, so if you buy an iPhone 4 now, I urge you to be very patient.
I hope I have clarified everyone now.
