Only members enrolled in the iPhone Developer Standard or Enterprise Program can access these bits of iPhone OS 4 and SDK by signing into Apple Developer Connection. The latest iPhone OS 4.0 Beta 1 is build 8A230m. Note that, if you have a jailbroken device, then this update is not for you. You will have to wait for the dev team/GeoHot to release iPhone 4.0 jailbreak.
Download iPhone OS 4.0 Beta Firmware
- iPhone OS 4.0 beta (iPhone 3GS) – iphone_os_4_beta_iphone_3gs_8a230m.dmg (364 MB)
- iPhone OS 4.0 beta (iPod touch 3rd gen) – iphone_os_4_beta_ipod_touch_3rd_generation_8a230m.dmg (354 MB)
- iPhone OS 4.0 beta (iPod touch 2nd gen) – iphone_os_4_beta_ipod_touch_2nd_generation_8a230m.dmg (306 MB)
Update: Guide to Jailbreak iOS 4.0 is here. make sure you read the warning within the post before proceeding.
Img credit: Engadget