To install a firmware Apple no longer allows, you need to trick iTunes with old saved SHSH blobs. Thus, if you wish to install 4.2.1 firmware, did you saved your 4.2.1 SHSH blobs through Cydia or locally with Tinyumbrella?
You are on the iPad baseband 6.15 so you can't use Greenpoison to JB the phone. You must use a custom firmware from Pwnage Tool(Mac) or Sn0wbreeze(Windows). There is a thread right on this page asking the same question read that, I've given the links to get the tools so search for iClarified on here and you should find the link. Are you on Windows or a Mac? I wouldn't worry about the SHSH blobs that will just complicate things I would just upgrade to 4.3.2 unless there is a specific reason you want 4.2.1? You will have to redo the Unlock which you will also find on iClarified. Oh what the hell here is the link again lol iClarified - Apple News and Tutorials go to Tutorials, iPhone, and you will go to Jailbreak first then once you're done JBing go to unlock.
You're on Windows so you'll need to use Sn0wbreeze. Search for iPhoneHeat.com and look for the 4.3.2 Sn0wbreeze JB. Then after you can go to iClarified and go to the unlock section.
aghhh! i tried to update/restore the phone with itunes, and it is freezing right after the firmware update now! i updated itunes first, rebooted, etc, and am still getting the error.
You just need to read the guides here. Like I just said, you have to make your own ipsw, so no, you can't use redsn0w. And like Ipheuria said a few posts ago, you need to use Sn0wbreeze to do that. He also gave you links to everything you need. Basically, everything you need has been posted on this thread; you just need to follow up on it.
No offense, but if you're not willing to research this part of it then you probably won't enjoy being jailbroken.
Actually, I forgot you were already jailbrokenin that case I'd suggest just staying with your current setup. If all you care about is the bootlogo, you might be able to find a theme in Cydia that will give you that on your current FW.
oh for crying out loud. now the phone is an eternal loop of recovery mode. i made an ipsw with snowbreeze, but can't implement it. anyone want an iphone 3gs 32gb?
oh man. the phone went into dfu mode (or so it said), but now i get another error message (1600) during the snowbreeze restore. that's all for tonight. i give up.
Is this a Windows problem? I have never ever had these types of problems with Pwnage Tool. In fact I've had times when Pwnage Tool would reload my firmware when iTunes wont load the official firmware. Ok lets try something add me on Twitter and DM me the details of your phone I'm gonna get the updated Pwnage Tool for 4.3.3 and make you a custom firmware. Make sure your iTunes is the most current version, only use Apple USB cables and plugged directly into your computer's USB port. If you've ever edited your hosts file or used Tiny Umbella please undo the change.
PS
Make sure you're an administrator on the computer. You can right click "Computer" and choose Manage. Then if it tells you that you don't have permission post up here.
Thanks, I'll do a twitter account later. I'll hit you up then. I keep getting either the 15xx, 16xx, or 31xx errors, depending on how far it gets. I even tried to do 4.1 again last night with the same results.
