If you find that you want to back down from the OS 4.0beta1 until it’s more useable, here’s how to do it:
Restore to official 3.1.2 or 3.1.3.
Your baseband won’t be downgraded, so you’ll get error 1015 at the end of the restore.
Use rslite or irecovery to get past error 1015. Using rslite, you’d do:
Your baseband will still be at 05.13 from the stock 4.0beta1, but FW 3.1.2 and 3.1.3 will work fine with it.
The current carrier unlocks will not.