Apple has just released another beta version of iPhone OS 4.0 firmware for developers, and this beta firmware is only supported with iPhone 3G, iPhone 3GS, iPod Touch 2G, and iPod Touch 3G. This is a fourth beta firmware and has built number 8A274b.

The first beta version of iPhone OS 4.0 firmware for iPhone, iPod Touch, and iPad was unveiled in the “Sneak Peek” event held at Apple’s Infinite Loop campus in Cupertino which brings lots of new features, support, and enhancements for both users and developers.

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Earlier this month Apple has released the third beta version of iPhone OS 4.0 firmware which has a build number 8A248c, you can read more about that here.

Don’t download or install this update on your device if you want to jailbreak iPhone OS 4.0 or jailbreak iPod Touch OS 4.0. So you’ve to wait until iPhone dev team releases a jailbreak for iPhone OS 4.0 firmware.

iPhone OS 4.0 Beta 4 Firmware – Download

The third beta version of iPhone OS 4.0 firmware is available for download for free for developers and can only be installed on a developer’s device.

• iPhone OS 4.0 beta 4 (iPhone 3G) – iphone_os_4_beta_4_iphone_3g_8A274b.dmg
• iPhone OS 4.0 beta 4 (iPhone 3GS) – iphone_os_4_beta_4_iphone_3gs_8A274b.dmg
• iPhone OS 4.0 beta 4 (iPod touch 2G) – iphone_os_4_beta_4_ipod_touch_2nd_generation_8A274b.dmg
• iPhone OS 4.0 beta 4 (iPod touch 3G) - iphone_os_4_beta_4_ipod_touch_3rd_generation_8A274b.dmg

Update 1: iPhone OS 4.0 has now been renamed to iOS 4.0 and Apple has also released a GM Candidate version of iOS 4.0 firmware. For complete change log, details, and download links go to this page

Update 2: The iOS 4.0 final version has just been released by Apple and is now publicly available for download for free for iPhone and iPod Touch. Head over to this page to download it.