This is for iPhone 3GS only.
First of all, YES you DO need the iBSS and iBEC files. Without them, you may never be able to jailbreak again once 3.1 is released. The reason for this is because Apple put a layer of protection on the hardware of iPhone 3GS. When you restore, it contacts Apple's server to generate a unique hash file, which is made specifically depending on your current hardware and your IPSW file.
Once 3.1 is released, you wont be able to jailbreak anymore, not even if you are already jailbroken. It was smart on Apple's part to make part of the restore process go through their servers, but bad for us.
But if you get BOTH the iBSS and iBEC files, the Dev Team will be able to develop a work-around for us to continue jailbreaking. Think of those 2 files as being your unique way to avoid Apple's
servers in the future. Without them, iTunes will ignore your phone and you'll be forced to have a stock iPhone FOREVER.
This is a particularly good guide for getting those files:
http://www.iclarified.com/entry/comments.php?enid=4400&laid=33#commentsanchor (windows version link at the top)
Yes, you will want to BACKUP your data, this process will ERASE everything. Once its over, you can restore your backup.
Think of it like this, if you dont do this NOW, you may NEVER be able to jailbreak again (even if you think you're special). And dont count on some genius hacker coming up with a work-around, the Dev Team themself (who practically invented jailbreaking) is saying this could be THE END... unless you have these 2 special files iBSS and iBEC, then its not the end.
Anyway, thats about everything I've learned from researching the past 2 days. Just got my own iPhone 3GS today and I've already got my 2 files. I'm set.
Good luck!
PS-- Owners of iPhone 2G and iPhone 3G are not concerned by this message. You can jailbreak your device forever (even if that means only 3.0 forever).
