Ya, do the process again. You will not need greenpoison since you have old bootrom. Just restore to the custom again an install cydia with redsnow after.
The first time you open cydia it will say initializing. It will the respring your iPhone making it look like it is stuck. Just wait it out, don't try to reboot during this.
Well, I think I am might in trouble now. iTunes won't recognize my device, and it keeps trying to reboot. I can turn it off, but then it turns back on by itself.
OK, iTunes is now restoring the custom firmware again.
Alright, back to booting Cydia and letting it do it's thing.
OK, weirdest thing. I got it!...? ... !
I am at 4.2.1, baseband 5.13.04, unlocked and on T-Mobile network. I thought I would have needed SAM, but not at all.
shanafan, could you share with me your custom 4.2.1 firmware? I've gone through the errors you have been mentioning here. My custom 4.2.1 firmware would leave my phone stuck in DFU mode instead of getting to the emergency call part.
Where are you exactly? Were you able to restore custom iOS in iTunes?
I used original 4.2.1 iOS and made it custom with PwnageTool 4.1.3. However, for some reason, PwnageTool was putting my device into a funky DFU modes that iTunes would recognize my device was in recovery, but always gave me errors when restoring. So, I used Redsn0w to only enter DFU mode and restored custom iOS in iTunes. With those steps, I was able to enter emergency call. I then ran Redsn0w again and told it to Install Cydia and all was good.