So, 4.2.1 has all sorts of errors esp. 10XX. so take it from me don't update your iPhone. I tried updating mine and it just messed up so I restore it back to 4.1. here's how: works pretty well.
1. put iPhone on DFU mode (YouTube - How To: iPhone DFU Mode - MacComm.tv
http://www.youtube.com/watch?v=ofpinyGlQ8I
2. open iTunes
3. you will recive message, that your iphone is in recovery mode
4. shift + restore, pick 4.1 fw (you can download from here Download iOS Firmware (
http://www.getios.com/))
5. wait for restore, then will be error 1015
6. your iPhone will in Recovery Mode, download Tinyumbrella (The Firmware Umbrella - TinyUmbrella
http://thefirmwareumbrella.********.com/ and kick out from recovery mode.
That's it. then follow the jailbreaking procedure on redsn0w.
http://tipsneeded.com/jailbreak-ios-...dows-mac-os-x/
NOTE: don't check just boot tethered right now. Check install cydia, battery percentage.
Unlocking the phone
http://hagardgsm.********.com/2010/1...3gs-3g-on.html