Download iOS 4.2.1

iOS 4.2.1 (3G): http://appldnld.apple.com/iPhone4/061-9853.20101122.Vfgt5/iPhone1,2_4.2.1_8C148_Restore.ipsw
iOS 4.2.1 (3GS): http://appldnld.apple.com/iPhone4/061-9895.20101122.Cdew2/iPhone2,1_4.2.1_8C148a_Restore.ipsw
iOS 4.2.1 (4): http://appldnld.apple.com/iPhone4/061-9858.20101122.Er456/iPhone3,1_4.2.1_8C148_Restore.ipsw