Getting mixed messages here.
Are hackers only working on sustaining jailbreaks, what about people without SHSH, are new hacks never going to be made?
I don't have SHSH btw, so does that mean I can NEVER jailbreak?
When you install your firmware (4.1, 4.2.1, 4.3), Apple requires you to check with their servers and the phone checks that the "SHSH blobs" that Apple provides the phone are accurate and that the firmware is one that's most recent. However, some smart people have found a way to save your SHSH blobs if you have jailbroken and trick your computer into thinking it's talking to Apple when it's really all taking place on your computer using a program called TinyUmbrella. TinyUmbrella then uses your saved blobs as confirmation for the phone that the firmware is the newest (even if it's not). Thus, people have jailbroken in the past can downgrade their firmware to any level that they have saved their blobs for (which Cydia, the "jailbreak store," will do automatically if you want).
As of 4.1, the jailbreakers have been using an exploit (the limera1n exploit) that is a part of the iPhone's bootrom, which is a part of the hardware more or less and cannot at all be changed. Thus, no matter what Apple does to iOS, this exploit can be used to jailbreak all iPhones. The tools used to jailbreak haven't been honed for the iOS 4.3 jailbreak to make it a really easy process yet for regular users, however, though that should only require minor tweaking and still use the same exploit.
However, this limera1n exploit only allows for a tethered jailbreak, meaning the phone must be re-jailbroken every time it is turned on or restarted. Currently, using other exploits in iOS, every firmware except 4.3 has an untethered jailbreak, meaning the devices can be turned on and off like normal. What we are mostly waiting for is the untethered iOS jailbreak, which this thread shows developers think the untethered jailbreak should be doable soon. Hope this helps, I'm not an expert, but this I think is a decent explanation of the basics of jailbreaking and where we stand today.
EDIT: We're also waiting for an unlock for iPhone 4's at basebands that Apple has used since iOS 4.1. The baseband is what the phone part of the iPhone uses and cannot be downgraded once upgraded. However, certain tools have allowed people to upgrade beyond 4.0.2 without upgrading their baseband (Tinyumbrella is one such workaround). Thus, when it warns people not to upgrade to 4.3, it means wait for the tools to adjust so that the upgrade can be done without updating the baseband. Once you upgrade your firmware (4.3), that's when you actually do the jailbreak. The purpose of an unlock is to allow you to use the AT&T iPhone on other networks like T-Mobile or European networks.
