Its confirmed! P0sixninja, member of Chronic Dev-Team confirmed that GreenPois0n will not only jailbreak all iOS devices but it will also hacktivate them so that you can bypass the iTunes activation screen and use your phone on any unofficial carrier after unlocking it with Ultrasn0w.
Update via @caiolbarros and @p0sixninja:
For those who don't know, GreenPois0n tool is based on a low-level bootrom exploit called SHAtter which will jailbreak all iOS devices including iOS 4.1 on iPhone 4, iPod Touch 4G and even iPad. According to pod2g, GreenPois0n will be out before Apple will release iOS 4.2 (Final) release which is due in this month.
Now we know that GreenPois0n jailbreak will be hacktivated one, it is still not sure whether it'll be a tethered or an untethered jailbreak. As soon as we'll hear any news about it, we will let you know. So stay tuned!
Update1: Chronic Dev-Team will Release GreenPois0n on 10/10/10 at 10:10:10AM (Sunday)
Update2: GreenPois0n will Jailbreak iOS 4.1 on iPhone 4, iPod Touch 4G, Apple TV & iPad
Update3: GreenPois0n Tool Released [Download for Windows & Mac]