Well as a user you might not want to read what Bootrom is. It's a heavy word. But I would appreciate if you understand this concept as well because in many articles to follow, we shall be using this word often.
iBoot/Bootrom is a read-only memory chip placed in your iPhone. It is the bootloader for your iPhone, which means it start the boot process of your iPhone (Steps which start from pressing the power button till reaching to the Springboard is taken care by Bootrom OR iBoot.
The 'Old Bootrom' version was exploited by '24pwn' (so you can Jailbreak them with 'Pwnage' tool till iOS 4. The 'New Bootrom' devices were released after 9th September 09' for which the exploit is yet to be found. That's the reason why there are tethered Jailbreaks' available for iPhone 3GS, iPod Touch 2G iPod Touch 3G via Blackra1n. Obviously Userland released 'Spirit', which was later patched by Apple.
Now you can think what happens when a Hacker manages to break the code of Bootrom? Since this is part of the hardware, Apple has to release a new hardware device altogether.
There are further exploits which are on the way to break the iBoot (like Greenpois0n by Geo Hot A.K.A George Hortz) which are trying to use the iBoot exploit of the latest iPhones which are running on iOS 4.2.1. This is done0 in order to ensure that an untethered jailbreak can be done on these devices which lets users reap benefits of both lower ROI (Return on Investment) and a flexibility to download applications from outside the App Store which otherwise is prohibited.
With the launch of Verizon iPhone 4, the excitement is much more because hackers want to exploit the new iPhone iBoot which would ensure that at least for that version of hardware devices (Verizon iPhone 4 in this case) will not be able to overcome the jailbreak with any software updates. In this case, apple will have to release a new hardware device (as hacking iBoot cannot be cured using any firmware or IPSW updates).
This space is getting all the more heated up with any new launches which apple does. There have been both tethered and untethered jailbreaks available for all the iDevices (be it iPhone, iPod, iPod Touch, iPad, Apple TV) and for all their versions.
Also, after Sony has filed for a law suit against Geo Hot for jailbreaking the PS3, apple has filed a similar case.
Source: ezinearticles.com