Seeing as blackra1n is only a tethered jailbreak, installing your own [custom] firmware is the way to go. But, (at least what happened to me) is that I constantly got 1604 errors while installing firmware of which I made using PwnageTool. As a short howto, here's what I did:
- Get blackra1n and run it. It'll put your iPhone in recovery mode. iTunes should be closed.
- Download or create custom firmware. If you are using PwnageTool, make sure to check off Activate so it is not activated. Just before it's done creating the firmware, click Yes to if your iPhone has been pwned before.
- Start up iTunes, and restore using the firmware you just made. For Windows users hold shift and click on Restore. For Mac users hold option. Make sure your iPhone is in recovery mode not DFU mode. That's the part that I forgot.
- iTunes should do it's thing and you'll be good to go.
- After I put the firmware on, I had no service whatsoever so I ran blackra1n again and I had service. If you have the 5.11.07 baseband, be sure to install sn0w in blackra1n. You might need to fiddle around with things.