what do you mean by this? surely if I use iTunes 8 and restore with my own firmware it cant be blocked?
+It is comming with 3.0 so I can use that if I cant update to 3.0.1
i mean iTunes (all versions that support 3Gs restore of any kind) contact the apple restore server before allowing a restore, no matter if you click shift and picked the file, the server then tells itunes, you are not allowed to perform the restore to 3.0 because 3.1 exists, and itunes then, you guessed it, refuses to do the restore
for now, when you get your phone, remain on 3.0 (don't even go 3.0.1)
jailbreak with redsn0w (if not already done)
upgrade to latest cydia
when startin cydia again it will ask you if it can put some restore related info on file on a cydia server for future use by yourself, allow this, cydia will now at the top say your phone data is "on file"
dev team very silently claims that the 3gs 3.1 os IS still exploitable through a new found exploit, which should enable them to jailbreak directly, but, if this is not possible, you need the on file info kept by cydia if you ever want to be able to downgrade to earlier firmwares again
as of now, the new 3.1 baseband for 3G cannot be unlocked, which means, all baseband bug fixes, you will not see, because you have to get a custom ipsw that doesn't upgrade your baseband...
again
you were warned