Iphone 3gs Baseband 06.15 stuck at recovery mode?
did exactly the same thing as you. I've been searching everywhere for the past 2 hours for a solution to the problem. I read somewhere that you can't kick out of recovery with 4.2.1 but you could with 4.1. The solution was firstly to go to C:\Windows\System32\drivers\etc\ and locate “hosts” file and add the line 74.208.105.171 gs.apple.com at the end (you will have to run with administrator privileges.) Then run redsn0w and tick just enter Pwned DFU mode right now. Once in DFU mode I downloaded a copy of the 4.1 IPSW from here
iOS 4.1 IPSW Download Sources - Softpedia ran itunes, pressed restore and shift and located the IPSW file and installed 4.1. You will probably receive the same error message as me when I tried to recover from 4.2.1 (error 1015). Ignore this, shut itunes, exit recovery with TinyUmbrella or as I did recboot and then you should be back into your iphone. Just a matter of then running redsn0w again but pointing to the 4.1 instead of the 4.2, but this time there is no need to tick the ipad bb install just the Cydia as bb is already installed. Hope it helps you as it did me. Write back if any questions.