For 3GS owners that want to Jailbreak, Please Read!
According to Geohot:
Apple has added a new layer of security to the iPhone 3GS. I mentioned it several posts earlier; it's the ECID field. When iTunes starts the restore process, they contact Apple servers to generate signatures just for your device. It's important you get these signatures for your phone before a new version of the software comes out. I had previously suggested doing this by dumping usb while the iPhone restores. But this is complicated.
Fortunately, the good folks at purplera1n are here for you, the end user who wants a jailbreak. Follow these instructions to generate a unique certificate for your phones iBSS. And don't delay, Apple may change their minds. To clarify, this is instead of a usb dump. Do this, and you are good!
1. Put your phone into recovery mode and connect it to your computer.
2. Using usbview on Windows(enable Config Descriptors), System Profiler on Mac, or lsusb on Linux, read your phones ECID. It's the 16 digit hex number after "ECID:"
3. Go to purplera1n.com, type it, and hit enter
4. Save the generated file for a purplera1nyday...