According to a recent tweet from Dev-Team member MuscleNerd, the carrier unlock solution is a step closer to completion for iPhone 4. The latest version of the carrier unlock requires Dev-Team to rewrite the entire baseband-unlocking code from scratch.
As part of Apple's redesign for the fourth-generation iOS device, iPhone 4 has a completely new baseband. The previous three generations of iPhone all shared the same baseband, explaining the relative speed of success after the original iPhone baseband was first unlocked (dubbed ultrasn0w).
The question of iOS 4 jailbreaking is still looming as well, though according to another tweet by MuscleNerd: "The next jailbreak from @comex is like first Spirit...all devices, all bootroms, latest FW, painless install." It is expected that jailbreaking will be made available along with the impending release of iOS 4.1.