The announcement it was made by p0sixninja but behind the project is a developer from the Netherlands who managed to jailbreak an iPhone 3GS on iPhone OS 4.0 beta 4 using PwnageTool to create a custom ipsw with which he restored through iTunes.
Unfortunately, many applications from firmware 3.x are not compatible with iPhone 3GS on iPhone OS 4.0, and if a jailbreak solution were available now, it would not help at all because you will not be able to use most of the existing applications in Cydia. The developer is working on this project to give Cydia app developers a chance to fix their apps before the official release of iPhone OS 4.0 and the jailbreak software.
In addition to the impossibility of running certain applications, the developer also explains that he cannot use the telephone function of the terminal, so this project is only in an early phase of development, but I am sure that it will take shape until the official availability of iPhone OS 4.0 we will have a version that will work just fine.
