According to the recent update by Kyle Matthews, founder and owner of modmyi.com, iPhone Dev Team and Planetbeing are working hard to unlock iOS 4 on iPhone 4 whos baseband runs a completely different OS called ThreadX which is an RTOS (Real Time Operating System) unlike previous iPhone models. This new baseband OS requires complete rewrite of Ultrasn0w code to unlock iOS 4 on iPhone 4.
iPhone 4 vs iPhone 3G vs iPhone 3GS Baseband OSs
Some words by Kyle Matthews:
The DevTeam and others have been checking through the iPhone 4, and have noticed the baseband runs a completely different OS than on previous models. The iPhone 3G and 3G[S] both ran Nucleus OS on the PMB8878 baseband CPU (aka XGold 608), where the iPhone 2G ran the PMB8876 (aka S-Gold 2). iPhone 4 uses the PMB9800, or X-Gold 618 - running a separate OS - ThreadX, an RTOS by ExpressLogic.
Another high-resolution screenshot and some videos tweeted by MuscleNerd shows that iPhone Dev Team is only a step away to iPhone 4 unlock.
DevTeam application running on the PMB8878 baseband processor.
Demonstration of Persistent Nucleus tasks in the iPhone 3G baseband SoC.
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