Press SHIFT on your keyboard at the same time with restore button on Itunes software and browse downloaded file from here: 2.0.0 (2G): iPhone1,1_2.0_5A347_Restore.ipsw 2.0.1 (2G): iPhone1,1_2.0.1_5B108_Restore.ipsw 2.1.0 (2G): iPhone1,1_2.1_5F136_Restore.ipsw 2.2.0 (2G): iPhone1,1_2.2_5G77_Restore.ipsw 2.2.1 (2G): iPhone1,1_2.2.1_5H1_Restore.ipsw 3.0.0 (2G): iPhone1,1_3.0_7A341_Restore.ipsw 3.0.1 (2G): iPhone1,1_3.0.1_7A400_Restore.ipsw 3.1.0 (2G): iPhone1,1_3.1_7C144_Restore.ipsw 3.1.2 (2G): iPhone1,1_3.1.2_7D11_Restore.ipsw 3.1.3 (2G): iPhone1,1_3.1.3_7E18_Restore.ipsw