Official Original Apple iPhone OS 3.1

Hi Friend, Below you can find the direct links to the iPhone Firmware Files for every released firmware version. Latest Version now is 3.1.

iPhone 2G

3.1.0 (2G): iPhone1,1_3.1_7C144_Restore.ipsw

iPhone 3G
3.1.0 (3G): iPhone1,2_3.1_7C144_Restore.ipsw

iPhone 3Gs

3.1.0 (3GS): iPhone2,1_3.1_7C144_Restore.ipsw

To Install, you need iTunes and u can download here.

iTunes latest version

Good Luck.